There is a mistake in the code.
I'm not sure why the compiler does not report an error:
Code:

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action enemy_fight // attached to the enemy
{
while(plBiped01_entity==null){wait(1);}
   	   distance = vec_dist (my.x, plBiped01_entity.x); 	
   	   enemy = me; // I'm the enemy	
   	   enemy.healthpoints = 100; // and I have 100 healthpoints	 
   	   while(!plBiped01_entity) { wait(1); }  // wait until the player exists	
   	   {

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Can you see it?
Do you see it now:
Code:

---

   	   while(!plBiped01_entity) { wait(1); }  // wait until the player exists	
   	   {

---

It should be:
Code:

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   	   while(!plBiped01_entity) { wait(1); }  // wait until the player exists	
           while(my.healthpoints > 0)
   	   {

---

Furthermore you may replace these lines:
Code:

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enemy = me; // I'm the enemy	
enemy.healthpoints = 100; // and I have 100 healthpoints

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With this:
Code:

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my.healthpoints = 100;

---

The enemy = my; stuff makes only sense if you have on enemy at a time.
But its useless if you use many enemies.

no errors or arguements anymore, and the enemy is alive, but he doesnt respond at all when i run into him, matter of fact, he is passable. also, he doesnt die, i shot him over a hundred times, but no affect. here is the code with the corrections.

Code:

---

var enemy_distance; // moves the enemy
var distance;
define sword_base = skill12; // using skill12, 13, 14 to store the sword_base coords
define sword_tip = skill15; // using skill15, 16, 17 to store the sword_tip coords
define healthpoints = skill18; // just another name for skill18
entity* enemy;
action enemy_fight // attached to the enemy
{
while(plBiped01_entity==null){wait(1);}
   	   distance = vec_dist (my.x, plBiped01_entity.x); 	
   	   my.healthpoints = 100;	 
   	   while(!plBiped01_entity) { wait(1); }  // wait until the player exists
   	   while(my.healthpoints > 0)	
   	   {
   	           if (distance < 200)  // the player approaches the enemy		
   	           {
   	                  vec_set(temp, plBiped01_entity.x); 			
   	                  vec_sub(temp, my.x);			
   	                  vec_to_angle(my.pan, temp);		
   	                 	my.tilt = 0; // I'm a maniac :)			
   	                 	enemy_distance.x = 5 * time_step;					
   	                 	enemy_distance.y = 0;			
   	                 	enemy_distance.z = 0;			
   	                 	ent_move(enemy_distance, nullvector);			
   	                 	ent_animate(me,"walk", my.skill19, ANM_CYCLE); // play walk frames animation			
   	                 	my.skill19 += 5 * time_step; // "walk" animation speed			
   	                 	if (my.skill19 > 100) {my.skill19 = 0;} // loop animation			
   	                 	if (vec_dist (my.x, plBiped01_entity.x) < 50) // if the player comes closer than 50 quants attack him			
   	                 	{
   	                          my.skill20 = 0; // reset "attack" frames				
   	                          while (my.skill20 < 100)				
   	                          {
   	                                  ent_vertex(my.sword_tip, 291); // sword tip vertex coords - get the value in Med					
   	                                  ent_vertex(my.sword_base, 306); // sword base vertex coords - get the value in Med					
   	                                  trace_mode = ignore_me + ignore_passable;					
   	                                  trace (my.sword_base, my.sword_tip); // trace between these sword positions					
   	                                  if (result != 0) // hit something, could be the player or another enemy					
   	                                  {	
   	                                           if (you != null) {you.healthpoints -= 4 * time_step;
   	                                  }											}					
   	                                  ent_animate(me,"attack", my.skill20, ANM_CYCLE); // play attack frames animation					
   	                                  my.skill20 += 5 * time_step; // "attack" animation speed									
   	                                  wait (1);				
   	                          }				
   	                          wait (6); // slows down the enemy and reduces the number of traces per second			
   	                  }		
   	          }		
   	          else // the player is farther than 200 quants away		
   	          {			
   	                  ent_animate(me,"stand", my.skill21, ANM_CYCLE); // play stand frames animation			
   	                  my.skill21 += 2 * time_step; // "stand" animation speed			
   	                  if (my.skill21 > 100) {my.skill21 = 0;} // loop animation	
   	          }		
   	          wait (1);
   	          	 	
   	   while (my.skill22 < 80) // the enemy is dead	
   	   {
   	           ent_animate(me,"death", my.skill22, ANM_CYCLE); // play death frames animation		
   	           my.skill22 += 1 * time_step; // "death" animation speed		
   	           wait (1);	
   	   }	
   	   my.passable = on; // the corpse can't be hit by the sword from now on
				}
}  

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Hi, Blink
I think maybe where you got my.passable = on;
should be in the while loop.

Code:

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while (my.skill22 < 80) // the enemy is dead
{ 
  ent_animate(me,"death", my.skill22, ANM_CYCLE); // play death frames animation
my.skill22 += 1 * time_step; // "death" animation speed
my.passable = on; // the corpse can't be hit by the sword from now on
wait (1);
}

---

still no change, thanks anyway.

There was some weird bracket stuff going on.
I rewrote and cleaned up the code a bit, now you should also be able to use it on many enemies:
Code:

---

define sword_base = skill12; // using skill12, 13, 14 to store the sword_base coords
define sword_tip = skill15; // using skill15, 16, 17 to store the sword_tip coords
define healthpoints = skill18; // just another name for skill18


action enemy_fight
{
	var move_dist[3];
	var distance;
	
	my.healthpoints = 100;
	
	c_setminmax(my);
	wait(1);
	
	while(plBiped01_entity == null)	{ wait(1); }
	
	while(my.healthpoints > 0)
	{
		distance = vec_dist(my.x, plBiped01_entity.x);
		
		if(distance < 200)	// the player approaches the enemy
		{
			vec_set(temp, plBiped01_entity.x);
			vec_sub(temp, my.x);
			vec_to_angle(my.pan, temp);
			my.tilt = 0;
			
			move_dist.x = 5 * time_step;
			move_dist.y = 0;
			move_dist.z = 0;
			c_move(my,move_dist,nullvector,IGNORE_PASSABLE);
			
			ent_animate(my, "walk", my.skill19, ANM_CYCLE);		// play walk frames animation
			my.skill19 = cycle(my.skill19+5*time_step,0,101);	// "walk" animation speed + loop animation
			
			if(distance < 50)		// if the player comes closer than 50 quants attack him
			{
				my.skill20 = 0; // reset "attack" frames
				
				while(my.skill20 < 100)
				{
					vec_for_vertex(my.sword_base,my,306);
					vec_for_vertex(my.sword_tip,my,291);
					
					c_trace(my.sword_base,my.sword_tip,IGNORE_ME|IGNORE_PASSABLE);
					
					if(you)
					{
						you.healthpoints -= 4 * time_step;
					}
					
					ent_animate(my,"attack",my.skill20,ANM_CYCLE);	// play attack frames animation
					my.skill20 += 5 * time_step;	// "attack" animation speed
					
					wait(1);
				}
				
				wait(6);
			}
		}
		else	// the player is farther than 200 quants away
		{
			ent_animate(my,"stand",my.skill21,ANM_CYCLE);		// play stand frames animation
			my.skill21 = cycle(my.skill21+2*time_step,0,101);	// "stand" animation speed + loop animation
		}
		
		wait(1);
	}
	
	// enemy was killed:
	while(my.skill22 < 80)
	{
		ent_animate(me,"death", my.skill22, ANM_CYCLE); // play death frames animation
		my.skill22 += 1 * time_step; // "death" animation speed
		
		wait(1);
	}
	
	my.passable = on; // the corpse can't be hit by the sword from now on
}

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But be aware: This code does not include that the enemy takes damage (reacts to a certain event), thus your weapon code needs to handle this.
I'm not sure how the templates work though.

well, it works sort of...i couldnt kill him, but he attacks, sort of, and he walks and stands fine. am i forgetting to add something to the code? maybe something i have to add to the plbiped code so the plbiped weapons will affect the enemy model and vice versa? what do you think Xarthor?

I think you need to add something to the enemy code.
However this is based up on the weapon code you use.
If your weapons use the "ACTIVATE_SHOOT" flag you simply need an event function for the enemy which reduces his health points when his event is event_shoot:
Code:

---

function enemy_events()
{
  if(event_type == event_shoot)
  {
    my.healthpoints -= 10;
  }
}

action enemy_fight
{
        var move_dist[3];
	var distance;
	
        my.enable_shoot = on;
        my.event = enemy_events;

	my.healthpoints = 100;
        //rest of the code

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works perfectly! thanks for your help. after i tweak it a little, i will post it for the community. you are a genius!