I don't have experience of CentOS but if nothing else works for you, this may be helpful.
I have Debian/Lenny and with the screwy Philips tv/monitor I use, Debian always boots up with the display halfway over to the left, losing the login dialog. It's almost certainly not Debian's fault - the Philips HD monitor adjusts itself to what it thinks is the correct sync (and most times it's way off the mark).
I discovered by chance that Ctrl-Alt-NumkeypadPlus or ...NumkeypadMinus rotates through the set of resolutions available with my elderly ATI 3D RAGE PRO AGP 2X video card, and usually one step forwards followed by one step back brings everything into alignment.
I don't claim that this will work for you - I just offer it as a last resort if nothing else works. Others may know whether such a feature exists under CentOS and whether my suggestion is a bunch of aardvark's kidneys.
Last edited by AncientBrit; 06-15-2009 at 10:50 AM.
Reason: Fix typos