How much did you pay for the CPU? it will be horrendously underpowered for most modern tasks.
what games do you plan on playing?
you mention GTA4 and BF3, and im fairly certain both will run horribly. they are both cpu dependent. GTA4 will run badly, but BF3 multiplayer will be nigh on unplayable.
really, i don't think you understand how weak that CPU is. Buying a more powerful GPU will just go to waste, cause the CPU will hold it back. Upgrading the CPU and buying a cheaper GPU will give you more overall performance for the same price, and then you have the option to upgrade in the future.
opf course, its your money to waste. but you asked the question for a reason. even if you don't like the answer, its still good advice.