Tom's Hardware guide is a good resource (
http://tomshardware.com )
for reviews of motherboards and video cards. You might want to check
out Tigerdirect for motherboard/processor bundles if you don't mind going
through rebate-hell.
Perhaps the hardest part is selecting the parts, especially processor
and motherboard. I would suggest AMD Athlon 64's .... they run cool,
are easier to install than pentiums, and a number of other reasons.
They are expected to go real cheap soon because Intel is releasing a new
worldbeater. (see Tom's H/W). The Intel will be $$$ so I'm staying with AMD.
Get a motherboard with SLI slots so that you can upgrade to dual graphics
cards later. I like Nvidia both for the motherboard chipset and graphics
cards.
Hope that helps.
Cheers -