It worked perfectly with a Abit KG7-RAID
Which is an AMD 761 based board, these have AGP support in the kernel.
its the 31-23 i think. 31-something. the kernel module is called NVdriver
Try using the newer drivers, they are up to version 41something something....
41.91. damn Gentoo hasnt been updated...
You could try the disabling AGP to start with though, as thats only 1 line in the config file and may narrow it down a bit.
im going to try
Option NVAGP 0 and 1 tonight (im at work)
Adam