I bought about 5 video cards trying to upgrade my old computer with the AGP graphics port. My advice, don't try to upgrade an old computer. Take all that money you are going to spend on upgrade parts and put that into a new computer. Go to somebody who really knows computers and have them build you a good gaming computer. That's what I did. My lowest frame rate on Millennium Force AyTrane was around 55 sitting on the brake looking at the station. Most of the rest of the ride was maxed out at 100 fps.
And coasteragent99 brought up a very good point. A 32 bit Operating System won't recognize more than about 4 Gigs of RAM. Windows 7 comes with both 32 bit and 64 bit OS discs. You can get VISTA 64 bit or maybe XP in a 64 bit version off E-bay. Make sure it's not a pirated version. You want the real deal.
I'm assuming you have an old computer with an AGP video slot. The new motherboards have PCI Express video slots which blow the old AGP slots out of the water, so to speak. The fastest AGP video card can't even compare with a good PCI Express video card.
So keep your old PC for it's older games and go out and buy yourself a new computer. Don't waste any more money on that RELIC!