Question about my 5770

Lol the 5770 is not weak under any circumstances.

It's mid-range, and that makes it easily capable of running MW2 on near-full settings I'd assume.

even on the 24" screen?

I know for a fact that the 5770 is better than the GTS 250 and my brother has a single gts250 in his dell and it runs modern games pretty dang well for the $125 he paid for it.

A 5770 is a very capable card. It performs slightly under a 4870. Would a 5850 perform better, yes of course. But by no means will a 5770 perform badly. I am assuming your 24" is either a 1920x1080 or 1920x1080 resolution. You most likely won't be able to completely crank most modern games, but you should be able to run everything fairly well with the card. I would suggest starting every game at the native resolution and on moderately high settings, with no AA. If it does well you can try and crank up the details. AA is nice, but to be honest all it does is smooth edges and at a nice high resolution I would prefer higher detail over AA.

To be honest, if you sent the card back hoping to get a 5850, it will be difficult as reseller stock for the 5850 and 5870 are pretty much none right now. I've been watching Newegg and haven't seen them come in recently. If they do it is very brief until people swipe them up.