well then i'm all set. and fooseball, you need a new motherboard that has pcie slots.
i'm not sure how to help you. at this point, if your system has only PCI slots, that to me suggests its quite old or it wasn't built with the future in mind. that means, new computer time. i think it's definitely your best bet if you're going to get a Gt, and possibly a new mobo.
dual if not quad core processor, 2 gigs of ram, a new hard drive, a new power supply because no doubt yours will be inadequate for such a powerful system, and probably you'll need a new tower to house it all, depending.
this is just a suggestion. you don't have to follow. but personally, i think just getting a new motherboard that will have the same crap put in it, just with a PCIe slot this time is a waste of money and time/effort.