JUst went through this, and they all ganged up on me and made me build my own. (OK, I'm a pushover). Somewhere with me at the top there is a question about buying a Dell or HP. Then a long and torturous piece on building one or having one built.
Here's the deal. Everyone I know with Dell has a problem or two, but seems to be otherwise satisfied. I get the feeling that extended warranties are a good idea with them or HP.
Don't listen to the Vista voices here. I'd get a Vista ready model, which means it will be set up with XP 64, and you have the choice to move to vista (for free or little money) or not.
I went with a AMD Athlon, which is coming up as a strong contender for the dual channel system. Dual Core and CoreDuo - both good. You need 1mg ram, now, no matter what, really, especially if you do gaming.
The consensus of those who made me do the build yourself thing again was that by getting a custom model you pay more and get more. I have to say that I am ecstatic, aside from a couple of details I can work out. There are a lot of companies that will build it with their components, and probably some near you. The danger in this, as with buying a Dell, is that it's easy to get carried away.
I nearly got mine from Central Computing in San Francisco (they ship). Guys name was Tim, and he was about as cheap as any web site without the grief.
For other resources try Tiger Direct.
Newegg
For good deals (and this is the best time be looking for any model) go to dealnews.
I got all my stuff from them, and I am pretty happy.
If you are uncomfortable with this, Dell does have some exceptional deals, and so does Walmart (Shudder)
If you are looking for rock bottom and think you will upgrade later, then there are a lot of relatively (amazingly ) cheap off the shelf models which may not last a long time, but will give you instant satisfaction. You can get a new one in a couple of years. (Not a good environmental decision, but sometimes necessity dictates.)