is this a good card for running cod4 at a playable frame rate ?

Get a Nvidia.

I think your framerate with those cards will rely mostly on the settings you run the game at. I bet if you google around for a review of those cards you'll find some benchmarks that include CoD4 and a bunch of other games. I was able to run the game just fine on an older agp card (x800XT), I just couldn't max out everything (most settings were fairly high though).

got a budget? cause if your going to spend like that idk, and it depends if your going to max out the game. I would recomend something in the 3000 series or better. 

i don't want to max the game really, i just want to play at a decent frame rate

What motherboard do you have?  Does it have a PCI Express slot or an AGP slot?

pci express, i think the hd radeon 2600 pro is pci express, right??

The 2400 really isn't a good card for gaming  It's more of a multimedia card.  The same goes for the 2600.  It's a bit better than the 2400 though.  The 3850 or 3870 is a decent ATI card.  It's not even that expensive either.  Just check Newegg