I had the same problem with ATI videocard on 64-bit CentOS 5.5. It was solved after installation of last "Catalyst" driver (After disabling SELinux: http://www.crypt.gen.nz/selinux/disable_selinux.html.) - ***I am not quite sure which driver you should use with nvidia. I would also advice to check for errors your installation "log"-file (It must located in your n-vidia directory somewhere inside  /usr/share/). For example, my problem was connected with GCC (I noticed errors inside log file and installed all necessary libraries).
 
Hope it helps.
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Best Regards,
Alexander Lebedev
 
I.P. Pavlov State Medical University
197022, Lev Tolstoy str. 6/8
Saint Petersburg, Russian Federation
 
tel.:+7-921-441-79-42
e-mail: awlman@rambler.ru
Skype ID: alexander.vl.lebedev