Not too sure about building your own... Great if you enjoy it, but when you tot it all up - and then add an OEM WIndows XP, there ain't much to be saved... (Though if anyone needs an Intel chip, PM me)
My own home build had every component other than the case (No, I am not joking) changed. And then, the XP buy (XP Pro £137 with no support afterwards) would have made it cheaper to buy online. I must admit, I did enjoy the build though. I now concentrate on learning to tie my shoelaces.
Conan