I'm not trying to be a jerk here, but I wouldn't use a PowMax PSU in any XP2500+ system, not even if I were given it for free 🙁 Maybe if it were powering a 500MHz Celeron or something, then yeah. 😛 Otherwise I bet I could make a nice wind-chime out of the PowMax...
:evil: ~ where's my tinsnips?!
Anyway, for practical advice, I'd grab me an Antec SL350 PSU, a Shuttle AN35N Ultra, and see if they'll play nice with your Creton RAM and your 2500+. If not, next thing is a stick of Crucial, Mushkin, Corsair or Kingston PC2700 (or PC3200 if you have overclocking in mind), and then a new CPU on the presumption that the CPU is toast. I dunno, this is a case where you can try nibbling on the troubleshooting operation or just bite the bullet and start over with the good stuff.
As an aside, remember that the thermal pad on a retail AMD heatsink is a one-use item. If you fired up the system, it's melted to fit the microgap between the CPU core and the heatsink base, and that's it. So if you remove the heatsink, remove all the used-up thermal pad and substitute a thin layer of high-quality thermal grease (Arctic-family ones are good quality).