First of all if your Ubuntu doesn't boot hold shift while booting, you'll see a kernel selection menu. Select rescure mode and then select safe Xorg. After that run aticonfig as foxmulder suggested. No need to delete xorg.conf though, it should be replaced by aticonfig.
If I simply remove the "new" card and boot up the rig everything works fine.
But then of course I can't initialize the new card since it's not plugged in :S
I will try your method of pressing shift while booting. Thanks for the input!EDIT:
I tried pressing shift while booting, got the kernel selection menu, selected recovery mode, and waited a minute or two for it to show me some options in a drop down menu.
Now I am looking at about 5 options. The one most closely related to xorg/video configuration seems to be "Run in failsafeX graphics mode"... do I select that one?