Comment 6 for bug 658258

Solved the problem:
installed nvidia-current via apt-get.
added the following lines to /etc/modprobe.d/blacklist.conf:

blacklist nouveau
blacklist lbm-nouveau

and the rebooted

Now the X server uses the nvidia driver, and with the correct resolution.
funny, if I enable the desktop effects, they get enabled, but the messagebox says that the effects can't be enabled due to my X ersver settings (but I can see the shadow and transparency of that messagebox... When I click "ok" the effects are disabled again)