It depends on the resolution that you play on, which is limited to what your monitor can display.
If you are gaming at 1280x1024 or lower, you should be able to see some pretty high settings playing smoothly. Your 2gb of ram might be a bit of a limitation, and adding another 2gb will give you some improvement as well, if your motherboard can support more.
If you are playing above those resolutions, you won't see max settings in many of the more demanding titles (like crysis or GTAIV) but not all games are that demanding, and you should get a good experience gaming on that platform in general.
If you are trying to play at 1920x1080 or higher, you will probably have to forgoe AA/AF to maintain smooth framerates.