I won't unselect the solution, but it's not worth it to upgrade that PC.
It can accomodate only a max of 4GB of DDR2-667/800 RAM, which is very slow(mine runs at 1GB/s, whereas dual channel DDR3 runs at 12GB/s+). Games will take a lot of time to load, if at all they do, and the CPU is going to be a bottleneck.
cub_fanatic, the processor you linked doesn't ship to India, which I think the OP is from. If he's from anywhere around there(pak, bangladesh, etc) I don't think he'd find a C2Q there either.
I use a C2D, and it bottlenecks a GTX 650, which I also use. I get 13FPS max on any playable scene on GTAIV(not counting tunnels).
Also personally, I don't think the processor will be able to handle the two games either, it gives me only 17FPS on LANoire, which is much less CPU intensive than FC4 and GTAV.