Hmmm...
Lots of good ideas. I've built and re-built 9 machines in the last five years. They're all in service, working fine. Five are shared more or less by Bite-sized trouble and I, and the others are virtually networked to my primary box.
I've used Newegg and Mwave, (even Tiger Direct once or twice), so the links from tinyvillager are nice to see. I agree that Dell is flexible in configuring to a customer's wishes, but their reliability is suspect, IMHO. Worse is HP; their machines are so proprietary as to be nearly impossible to alter. (They rivet drives in place!)
Unless you need to live on the bleeding edge of tech, I've found that it's easier to build solid, robust boxes using components that have been out long enough to get thorughly discussed in their respective forums. I also wait for the inevitable price drop!
Frankly, I've learned everything by trying. We was all newbies once, after all...
After I overcame the terror the first time I cracked open a case, it was Wahoo! from there.
OEF