Ummm, i don't know if you guys read up above, but i went through this stuff for weeks. In the end YES i do have the Nvidia drivers installed on Slack 9.1 (2.4.23) and the AGP and GLX works fine with the K8T800 chipset and AMD64-agp. I also had the the 2.6.0-test11 kernel working fine with ONLY PCI enabled with the Nvidia drivers. As i said before, the problem is that "I" couldn't get 2.6.0 to like my agpgart and AMD64. I couldn't get agp to enable. Well as i posted above (i was trying to help other people - you know, save them some time), i got the agp to work with the Nvidia 4620 beta driver and on 2.4.23 kernel with AGP enabled - sweet!!
Gentoo Linux-64, AMD64 Athlon 3200, Asus K8V Deluxe, 1 gig(3200 400mhz) ram, GeForce FX5200 128, HP 400i DVD+R+RW, HP ScanJet 2200c, Epson Stylus C84, JVC DRV3000U (firewire - usb), Kodak CX6330