haha im looking at upgrading as well for this game alone :)
but as far as your video card goes, Im sure it will handle GTAIV like a champ. The Radeon HD6750 1gb is a good card for the price, but requires a PCI Express 2.1 x16 and your mother board only supports 2.0. Gotta watch out for that one, the 2.1 demands more power then the 2.0 and now the even have 3.0 out. as for your other things the links are not working.