I have been fighting video problems with Debian for a couple of weeks. I corrected the /etc/X11/xorg.conf file here.
If it looks familiar it should! This is the /etc/X11/xorg.conf file from the 64 bit Ubuntu 10.10 Livecd. I put it onto a usb flash drive, used sneaker net (which means I pulled it out of one machine, walked over, and put it into another), and copied it over. Restarted the gdm3 on 64 bit Debian Squeeze. I have full use of the hardware graphics capability and monitor sizes.
Using Ubuntu to fix Debian. Oh! I so love irony.
Thanks Joe for this crazy idea. But it worked!
Wayno