AGP cards based on the Radeon4000 can be a real pain. Catalyst drivers don't really support that configuration and all the AGP cards with these GPUs are the result of GART tinkering by the card vendor. I bought two of these to try and breathe new life into some old P4 systems I had for HTPC use but got tired of pulling my hair out to get anything resembling a stable set of drivers running.
In 2012, spending any money on AGP just isn't a good idea. If you're lucky, you might find a good AGP card (GF7800 or X1600) on eBay or Craigslist but even then, it's going to be 5-6 years old and it's hard to find one for a fair price since most of the people who have them know there's someone out there who just has to have one and will pay stupid money to get it.