Sorry, Hammyton, that PC100 RAM is useless if you are upgrading to a XP 2000+. While I am not very familiar with the AMD route, I think you would need a minimum of PC2100 memory. While its pricey, I'd recommend PC3200 from Corsair.
The thing to remember with power supplies, is not to get some cheap off-brand - Don't skimp on the PS. Depending on how many devices (drives, cards, fans, etc.) you have will determine how much juice you need. If you are running the minimum amount of devices, then you could probably get by with a 300W PSU. However, if you buying it new, I'd just go ahead and spend the extra $$$ for the 350W and not worry about it....