From the rockstar web site:
Minimum requirements:
Processor: Intel Core 2 Duo 1.8Ghz, AMD Athlon X2 64 2.4Ghz
Memory: 1.5GB
Free Hard Drive Space: 16GB
Video Card: 256MB NVidia 7900 / 256MB ATI X1900
DirectX 9 compatible Stereo Sound Card
Recommended:
Processor: Intel Core 2 Quad 2.4Ghz, AMD Phenom X3 2.1Ghz
Memory: 2GB (Windows XP) 2.5GB (Windows Vista)
Free Hard Drive Space: 18GB
Video Card: 512MB NVIDIA 8600 / 512MB ATI 3870
DirectX 9 compatible Surround Sound Card
So I guess you probably can. I'm not quite sure what your video card is whit what you said tho. There are a lot of options in this game to scale down the graphic to accommodate weaker machine (distance of view, detail quality, light, shadows and even traffic density).
Still, check you graphic card model (not just ram amount) to be sure