Yep, the post above it right. I thought I could upgrade a part or two here or there, but basically built a completely new system with only a couple of canabilized parts off the old pc. My new pc IS upgradable. Try
http://www.tomshardware.com for their pc building guide. Its not all inclusive, but it is a good place to start your research.
As far as the motherboard goes, I would go with asus over soyo, but that is just my opinion.