|Standard PCI was replaced by AGP, AGP was replaced by PCI-express. Stay away from standard PCI video cards, they are useless when it comes to gaming. There are still AGP video cards available but the majority of them aren't very good for gaming & the good ones that are available are usually very expensive.|
The Radeon HD cards were designed for PCI-express. Some of them were retrofitted for AGP, but they don't work all that well due to driver issues. If you check the feedback on the link posted above, the biggest complaint is problems with drivers. I recommend you stick to GPUs that were designed for AGP.
Unfortunately you just missed out on an excellent deal for a Radeon X1950 Pro that was on sale at TigerDirect for just $22. It's a true AGP gaming card that's just as fast or faster than the HD 4650. It orginally sold for $250 back in the AGP days. Here's the link currently showing it as unavailable:
Visiontek Radeon X1950 Pro / 256MB GDDR3 / AGP 8x / DL Dual DVI / HDTV / Video Card (Refurbished) - $22