[Sand]

I build my own PCs -- which I don't recommend unless you intend to make a hobby/business of it. The following places will give you a good idea as to what components are important, which can help when buying a pre-built system.

Arstechnica.com Posts decent buyers guides, as does anandtech.com. I go to hardocp.com for detailed info (they have a buyer's guide as well), but that is a hardware enthusiast's site and not for the faint of heart!

For buying components, I heartily recommend newegg.com.