overclocking a visiontek gf2 mx400

i have a visiontek geforce2 mx400 (its called xtasy), it does not have a fan on it, jsut a heatsink. Do i need to put a fan on it or something in order for it to overclock? if so... do i have to take off the heatsinnk or just put the fan on top of the heatsink if that is possible. My geforce2 is 64mb PCI (i have a p3 450, it had integrated video memory so no agp port : ( )