Also, where is the agpgart patch you mention? I assumed it would be in the source tarball, but all I see is code for audio and network.
Finally, I'm curious--how likely is AGP support for non-nVidia cards?
It will be a part of the next nForce driver release. It's also been given to the AGPGART maintainer, so it should be in a kernel soon.
The patch will enable AGPGART support for nForce/nForce2; it's not card specific.