@Prog_Plus_plus:
Yeah you're right about the 50, however changing the order of the instructions does help too
Oh and good explanation about the % Operator.

@topic:
here is an update, tested version:
Code:

---

action arrowBox
{
   var counter=0; // counter has initial value of zero
   while(1) // continue firing indefinitly
   {
   	counter += 1;
       if(counter == 50) //play with this number(amt of time b/t firing an arrow
       {
           you = ent_create(arrowMDL,my.x,arrowFly); //create new arrow
       }
       counter %= 50;
       wait(1);
   }
}

---