I have had a similar problem when upgrading to 2.6.20-13 kernel. It appears that the NVIDIA driver for this kernel is broken, at least as far as this card is concerned (I have the same). I have tried a fresh install to investigate a virgin feisty installation (my default is heavily modified) and have found that the "nv" driver works (but with reduced functionality as expected), but as soon as I try to enable nvidia (including hand-editing xorg.conf) the x-server fails to start. Unfortunately as this is a proprietary module it is probably out of the hands of the ubuntu team to fix, unless it's a packaging error.
-- After my last Feisty update I could not start X server. https://launchpad.net/bugs/93318 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
