+1 on what linkin says, but if you do get it working it probably won't be veryh good if it is the specs in your sig.
your CPU will have alot of work and you have probably not enough memory. To play it well you really need a high clocked dual core (which you have) or ideally, a tri or quad core CPU. system requirements are here:
OS: Windows Vista - Service Pack 1 / Windows XP - Service Pack 3
Processor: Intel Core 2 Duo 1.8GHz, AMD Athlon X2 64 2.4GHz
Memory: 1.5GB XP / 1.5GB Vista
Graphics: 256MB Nvidia 7900 / 256MB ATI X1900
DirectX Version: DirectX 9.0c Compliant Card
Hard Drive: 16GB of Hard Disc Space
Sound Card: 5.1 Channel Audio Card
Other Requirements: Initial activation requires internet connection; Online play requires log-in to Games For Windows - Live and Rockstar Games Social Club (13+ to register); software installations required including Adobe Flash, DirectX, Microsoft’s , Games For Windows - LIVE, and Internet Explorer.