A far easier thing to do that is supposed to stop the "X freeze" is disabling AGP support. This reduces graphics performance - only you can decide if that's ok for you.
I'm currently trying this to see if it works for me. If it does I may accept the loss of performance until the underlying bug is resolved.
To turn off AGP support the the nvidia driver add
Option "NvAGP" "0"
section of your /etc/X11/XF86Config-4. The same section that contains
This is documented in /usr/share/doc/NVIDIA_GLX-1.0/README APPENDIX F