Upgrading Video card what will work?

Nope, both of those cards should work just fine in your rig.

I have 3 gb ddr2 ram(32 bit vista), the chipset is an Intel Core 2 Duo 1.86, gateway brand computer. Not sure on the motherboard yet, but like I said it does have pci express slot. The psu brand is antec. I am not that knowledgeable about over clocking the cpu, I wouldn't know what to do or where to start.