If you want to use openWii you might have an easier time finding a PIC 12F629 or PIC 12F675 to work with. I am not sure how to build a programmer for this such chip as I found an ATMega8L from futurlec.com. Word of warning, futurlec is slow but I did get everything I ordered for cheap.
If you have never soldered before I would suggestion practising on an old video or sound card. I practised on one for a few hours while I waited for my parts. It was very fun to put the Chiip project together though and you definitely get a sense of pride when you are done.