Thanks for the input.
Here's what works and what doesn't work on my machine:
MSI KM2M Combo-L (Via KM266 chipset)
ASUS FX 5200 64MB
Fedora Core 1, Vanilla 2.4.23 kernel.
Oops when starting X. If I set NvAGP to 1 in XF86Config it appears to work OK, but this basically disabled AGP as I have agpgart compiled into the kernel. I didn't try setting NvAGP to 0, but I suspect this would also work. glxgears results in about 1300 fps. I'm using the Composite video out as the display device, and in X the display was pretty jittery. Overscan does NOT work.
Everything appears to load OK. However, running glxgears results in the X server crashing. TV-out slightly less jittery than -5338. Overscan does NOT work.
Everything appears to load OK. glxgears results in 2000 fps. TV-out very solid, very little jitter. Overscan WORKS!
The moral? The latest drivers aren't necessarily the best ones to use for your system.