found this... maybe it helps

Code:
// turn an object to an destination
function turnto(ENTITY* pe, var* ppos, var* p_speed){
var lva[3];
	
	vec_set(temp, ppos[0]);	
	vec_sub(temp, pe.x);
	vec_to_angle(lva[0], temp);
	c_rotate(pe, vector(ang((lva[0])-(pe.pan))*p_speed[0]*time_step, ang((lva[1])-(pe.tilt))*p_speed[1]*time_step, ang((lva[2])-(pe.roll))*p_speed[2]*time_step), IGNORE_ME|IGNORE_PASSABLE);

}