As always suggestions on how to improve this instructable are always welcome
Also, here's a random site that I StumbleUpon'ed. It's pretty out-of-date, but it does have purty animations
Step 1: Decide what the computer needs to do
You also need to decide whether this computer will be one where you build and let it sit at those specs or whether you will upgrade it over time. I prefer to choose parts that will enable easier/cheaper upgrading down the road.
Decide on a price point. If you name a price, you can probably build a computer at that price, although it might not be able to do all that you need/want it to do.
Decide on a timeline. If you have no need of the computer for the next several months, you can sign up for newegg's shell-shocker deals emails and wait for the deals on the parts that you want, as well as watching amazon, tigerdirect, ebay, overstock, and woot!. Generally the more time you have to wait for deals, the cheaper you can get a computer, although if you take too long you might run into issues with returns (newegg has a 30-60 day return policy for most items, after that your only option is to RMA a defective part for a working one from the manufacturer), etc.