What resolution are you playing at? If you are playing at 1900x1080, than you'll be playing on low settings but it will play it around 30fps or so. If you are playing at 1280x1024, you should be able to turn the settings up some to increase your gaming experience.
Even the highend graphics cards like GTX 295 and ATI 4870x2 have problems with some settings on Cyrsis. If you are looking at COD4 or games like that, you'll be able to enjoy your gaming with the ATI 4770. You might not able to have all of the "eye-candy" on but at enjoyable settings.