I used PH_RIGID for the box and sphere, but the level is PH_STATIC (created by physX_open()). Every frame, I move the box downward, but it is prevented from touching the ground. Below is a modified source code, and you can try to move to the left, but the PH_CHAR box can't touch the STATIC wall.

Code:
#include <acknex.h>
#include <default.c>
#include <ackphysx.h>

void main()
{
	physX_open();
	
	// Set shadow
	shadow_stencil = 2;
	
	level_load("PLATE.WMB");
	wait(3);
	
	// Set camera
	vec_set(camera->x, vector(-265, -30, 90));
	vec_set(camera->pan, vector(0, -11, 0));
	
	// Create player
	ENTITY *e = ent_create("CUBE.MDL", vector(0, 0, 100), NULL);
	//vec_set(e->scale_x, vector(2, 2, 2));
	//vec_set(e->scale_x, vector(0.5, 0.5, 0.5));
	set(e, SHADOW);
	pXent_settype(e, PH_CHAR, PH_CAPSULE /*PH_BOX*/);
	
	// Create
	ENTITY *box = ent_create("CUBE.MDL", vector(20, 20, 50), NULL);
	set(box, SHADOW);
	pXent_settype(box, PH_RIGID, PH_BOX /*PH_CAPSULE*/);
	
	// Player movement
	var player_gravity = 0.1;
	var player_speed = 0;
	
	ENTITY *sphere = ent_create(SPHERE_MDL, vector(-20, 0, 100), NULL);
	set(sphere, SHADOW);
	pXent_settype(sphere, PH_RIGID, PH_SPHERE);	
	pXent_setmaterial(sphere, vector(100, 0, 0), vector(100, 100, 100), vector(0, 1, 0));
	
	// Create static wall
	ENTITY *wall = ent_create(CUBE_MDL, vector(0, 40, 20), NULL);
	vec_set(wall->scale_x, vector(5, 0.5, 5));
	c_setminmax(wall);
	set(wall, LIGHT | SHADOW);
	vec_set(wall->blue, vector(150, 0, 0));
	
	pXent_settype(wall, PH_STATIC, PH_BOX);
	
	
	// 
	while(1)
	{
		// Add gravity to speed
		player_speed += player_gravity;
		
		// Move charachter downward
		pXent_move(e, NULL, vector((key_cuu - key_cud) * 2 * time_step, (key_cul - key_cur) * 2 * time_step, -player_speed * time_step));
		
		// Debug entity z
		DEBUG_VAR(e->z, 10);
		
		VECTOR temp;
		vec_set(temp, e->x);
		temp.z -= 1000;
		my = e;
		
		var dist = c_trace(e->x, temp, IGNORE_ME | USE_BOX);
		DEBUG_VAR(dist, 22);
		
		// Distance to ground
		DEBUG_VAR(e->z - dist, 34);
		
		//DEBUG_VAR(pX_stats(1), 50);
		
		// Wait frame
		wait(1);
	}
}