firstly, this should definatly be in the console forum.
secondly why would you want to hack your dc controller to your ipac? to use your dc controller to play games on your pc? if thats the case just buy an adapter from level 6 or somewhere like that.
if you want to hook your arcade controls up to the dc, thatsa differetn story, as wel las if you want both the ipac and the dc controls always hooked up(which iw ould recomend against, its a huge pain, just rig up a quick way to swap controls)
eiher way both of thse have been covered extensively i nthe consoles forum.
good luck