I upgraded from Debian squeeze to wheezy. My box contains an old graphics card not supported by current Nvidia drivers for distros newer than lenny (NV5M64 [RIVA TNT2 Model 64/Model 64 Pro]), so in my /etc/X11/xorg.conf, I had Driver "nv" specified in squeeze (which didn't seem to work after the update to wheezy).
After reading the internets for a bit, I found that my card should be supported by the nouveau driver. Replacing Driver "nv" by Driver "nouveau" in my xorg.conf still didn't produce a useable X.
I read a bit more and made sure to remove any and all proprietary pieces of Nvidia stuff, including drm and whatnot. Just going with the non-free drivers, as suggested in many internet posts, was no option: Remember that Nvidia dropped the driver for my TNT2 card for everything newer than lenny. Anyhow, still no success.
The only way I got any type of X working was using the "vesa" driver, but only in a resolution lower than my LCD monitor's native 1280x1024.