Thanks for your interest.
Unfortunately, the link you provided me was far from my situation (Single 32bit CPU, kernel 188.8.131.52 , latest non-beta drivers).
I also checked http://www.nvnews.net/vbulletin/showthread.php?t=46678
and I'll try to restart system up to XORG yet to begin, then startx verbose and get a log.
Unfortunately, it seems that problem does not occour if I login to a multi-user mode without X then I start X manually.
I'm starting to think that the system may be under heavy load when X starts concurrently with normal bootup process.