Thanks van, your post helped me find out a lot about how the XF86Config-4 file works. I should already know this stuff, but GL stuff is only for my home kit, and most of my jpro work is DB and server work. Anyway, I copied the useful bits to my XFConfig, and it worked. I could play with a lot of the GL toys, no problem.
Still, I had two problems. One, and I'm assuming it's the custom mode, is that my screen was really off center and narrow. Where did you learn (I know I need to RTFM) how to make custom modelines? Also, your setup looked (at least on my system) to be a 800x resolution. I'm using 1024x728 right not, with the nv driver.
As a side note, I'm not totally sure about the custom mode stuff, because even when I #'d it out, it still came up like that.