Hello!
Have you run Apple Hardware Test yet on the machine? This test is included on one of the DVDs that came with your computer. This may help further diagnose. However the power supply certainly shouldn't be that hot!!!
iFixit does not yet have a guide for this machine. You can use the guide for the [guide|1006|20" counterpart] to get where you need to go.
The part you need depends on your machine. If you do not know which machine you have, check out the [http://www.ifixit.com/Info/ID-your-Mac/774|ID Your Mac page]. If you have a 2.4 or 2.8 GHz (EMC 2134), your part number is 661-4478. If you have a 2.8 or 3.06 GHz (EMC 2211), your part number is 661-4665. Plug these numbers into the search box in the upper right corner of [http://www.applepalace.com/|Apple Palace] to find your part!
I hope this helps!