How much $ for a decent gaming PC?

My PC sucks. I've been toying with the idea of building a new one and using this one for music/web browsing or running Linux on it for fun. (I'm aware of how geeky that sounds.)

If I wanted to put together a decent gaming rig that would play the games coming out right now, like Half Life 2 and Doom 3, how much money would I be expected to spend? Keep in mind I'd be building it myself.

Also, is it better to go with the motherboards that have the chip and fan already attached? Probably cheaper, but worse for updating.

On my way to PriceWatch...

EDIT: Suggestions on components would be VERY welcome, since I haven't done anything like this in about 9 years.

For Doom 3, I'd strongly suggest a Radeon 9800 (possibly Pro) and 1 GB or Ram, though that will jack up the price a few hundred dollars more than Armbreaker's suggestion.

But, I guess that's the much do you have to spend? That's really the limiting factor.

You can have an absolute killer gaming rig that won't need upgrading for a couple of years for 800.

Yeah you can build a very decent gaming system for under $1000. Here's the first place I'd start: Don't forget to subtract what you already have from the price (keyboard, mouse, monitor, Windows OS, etc). And also keep in mind you can find better deals then some of the stuff they have listed, like they're paying $70 for an 80 gig drive, that's $0.88 a gig. However if you look in the weekly ads in your area every week they have hard drives that are $0.50 a gig after rebates. And if you already have an extra hard drive, well that's even better.

Give a us a price range of how much you're willing to spend and we can probably design a system within that budget or at least tell you that you should save up cash for a little bit longer before looking to build