This error is irrelevant - I have one too and live.
Whats more important, do you try installing nVidia driver while X server is still running and nouveu module is loaded? How unwise...
Reboot to recovery mode and install it from there (and configure xorg.conf with installer tools when prompted - unless you have your own good xorg.conf for nVidia).
And there is error for kernel sources configuration that's no good and need to be fixed.
Did you installed kernel-headers?
Did you followed sticky thread? http://www.nvnews.net/vbulletin/showthread.php?t=72490
sudo apt-get build-dep nvidia-graphics-drivers