The collision events with physX are activated with 'pXent_setcollisionflag'

Code:
pXent_settype ( ent, PH_RIGID, PH_SPHERE );
pXent_setcollisionflag (ent, NULL, NX_NOTIFY_ON_START_TOUCH ); //trigger EventImpact on collision with level
ent.event = EventImpact;