It's free and already built, but I won't have it until Sunday, so please don't tell me to check CanYouRunThis?, as I know some of you will. Here are the specs, just name off a few recent games I should be able to play.

2.0GHz Core 2 Duo
3GB Non-ECC, 677MHz DDR2
256MB ATI Radeon HD 2400 XT, which I'm assuming is PCI (The invoice my dad sent me doesn't say)
XP Pro

The orange box should be very playable with AA off. Looking at most benchmarks it seems that you're good if you don't use AA.

You could probably handle CoD4 on medium settings with AA off.

Hopefully that's good enough. Those are just some games that I can handle (on lowest settings) with my integrated card, and looking at benchmarks, yours is quite a bit slower than the 8600 (which my friend has and runs those both on highest with high AA). Don't expect to be playing anything on highest settings, though.

And this all depends on your resolution. These were all at 1280x1024. You could probably run them better at lower resolution.

Most anything on low or medium-low settings. The graphics card wil hold you back most. If you're in the USA, it's an easy upgrade to a Radeon HD 4650 or HD 4670.

It sais they are on their profile.

http://www.newegg.com/Product/Product.aspx...N82E16814161252

Or you could do crossfire. If you were to spend the money, of course. It depends on the mobo really though...

I'd probably go with the card Caboose posted, if I were to upgrade. Cards these days are pretty cheap, aren't they?

Yes. Even a $50 card nowadays can play most games on high settings.

I popped open the case today and it's a PCI-E x16. Would that be okay, or would I still probably want an upgrade?

You can still run the card that Caboose posted on that motherboard, but the card probably won't take full advantage of its capabilities.

I personally would upgrade it anyway, maybe with this motherboard (or something cheaper).

Yep those are the good slots.

You can do what bob says and get one of those cards, then just swap them out (can you do crossfire with two different cards?).

Nope. I only have one x16 slot. The other is x1.

Oh, no crossfire then.

You can get a 4650 for ~$60.

For crossfire i would recommend at least x16 and x8, or x6. There's only a few fps difference in the end, and if the mobo is a good price then it's not a deal breaker.