I've been trying to make my Fedora 4-64 box work with twinview.
If I modify the xorg.conf file to use
Driver "nvidia"
and restart the X server (ctrl-alt-backspace) or with init 3 and then init 5, then twinview works like a charm.
Prolem is that every time I reboot the machine the xorg.conf file gets changed to the wrong driver
Driver "nv"
and then twinview is gone and one of my monitors goes blank.
How can I prevent xorg.conf from getting changed?

Sounds like your having problems saving your config. Do you see the nvidia splash screen appear when you start the "X" server?? Once you start the x server you should see the nvidia splash screen appear.

This is what I do.

Open a terminal and change the x run level from 5 to 3
Then I reboot my box.
From the command line log in as root and install the nvidia driver.
sh NVIDIA(of course tab thorugh the rest of the command.
After the driver is installed (you might need to install the kernel development tools.)
Then open the X config and delete the "GLcore" (GL something) and "dri" plus you need to change nv to nvidia.
Save your settings.

Then finally change the run level to 5 and reboot the box.

All should be well and you should see the nvidia splash screen as X starts.

thanks!
I was finally able to make use of my two monitors!