Well, I think I see a culprit to your problem.
01:00.0 VGA compatible controller: nVidia Corporation G71 [GeForce 7900 GT/GTO] (rev a1)
02:00.0 VGA compatible controller: nVidia Corporation G71 [GeForce 7900 GT/GTO] (rev a1)
05:07.0 VGA compatible controller: ATI Technologies Inc RV280 [Radeon 9200 PRO] (rev 01)
X is having a hard time with your multiple vga cards!
Is the ATI card onboard? Can it be disabled?
Searching the *buntu/Mint forums / bug reports, I found that to install Jaunty/Gloria the members had to remove all but the Primary card, install went fine, then they installed the NVidia Restricted drivers, rebooted to make sure all was okay, then they shut down to re-install the secondary card, worked fine from then on!
Must be something in X or the kernel, as the members stated that it worked out-of-the-box on previous versions!