Saad Shakeel :
without over clocking 30 + ?
25-30 FPS possible at 800x600 resolution. You PC almost meets the minimum requirement. Only the processor lags behind.
Minimum Specifications:
OS: Windows Vista 64-Bit or later
Processor: Intel Core 2 Quad Q6600, AMD Phenom 9850, or newer
Memory: 4GB RAM or above
Graphics: GeForce 9800 GT 1GB or newer
DirectX: Version 10 or above
So the best way to go about it is to follow the NVIDIA's Official Grand Theft Auto V PC Graphics & Performance Guide, which would immensely help in getting the best possible frames for your setup.
http://www.geforce.com/whats-new/guides/grand-theft-auto-v-pc-graphics-and-performance-guide
Don't hesitate to experiment with the settings discussed in the above guide, to get best possible experience out of your setup.
Also update your card to NVIDIA's GTA V exclusive driver before you run the game and try out any of the above said options.
GeForce Game Ready Driver for Grand Theft Auto V -
http://www.nvidia.com/download/driverResults.aspx/83819/nl-nl
Note: Try ask all your questions in a single go. Also its better to keep your questions minimal per thread, so that its easy for people to follow and give you speedy better solution.
Cheers!