Basicly all GeForce3s and GeForce4s use 1.5v agp. Most GeForce2s use 1.5v agp, but a few do use 3.3v, but not many. And all ATi Radeons use 1.5v agp. If your looking at playing games, which i'm assuming you are you should really be only looking at GeForce4s and Radeons anyway so this limitation should not really be a problem. I hope this helps.
Looney