ok, I think I got it. There seems to be a problem between AVWizard and the 173 nvidia drivers. When using "nv" in the xorg.conf, then the AVWizard comes up and I can go through it (why it comes up twice however, I have no idea). Once the wizard is finished and the MD reboots, I get the message, that Opengl cannot be loaded. Reverting "nv" to "nvidia" and restarting the md once more does the trick however.