Not with that system unfortunately. A dual core system with only 2GB will struggle with GTAIV.
GTAIV has a very strict limit of what it runs well on, only high end CPUs do well in it, and that's only 40fps+. Unfortunately graphic level does not affect FPS as much in other games, since it seems to be doing a lot of AI and physic work, which a good CPU does well with, especially quad core and above.
With my system I barely get 30fps, with a Phenom II x4 940 + Radeon 4890 at every setting.