I'd also suggest
http://www.pricewatch.com/ for components. Its an index of many stores and lists old and new components. Only thing to watch out for is sometimes things get listen in the wrong catagories, but generally a very useful site.
Btw, for about maybe as little as 300 bucks, you could put together a nice Athlon 64 combo (2800+, any old Ath64 mobo, 512 MB PC 3200 DDR RAM)