I spent a little while on this problem, with no console output I`ll take a guess
VidModeExtension ,dga mouse errors ?
I had to add this section to my xorg.conf (/etc/X11/xorg.conf)
Option "omit xfree86-dga"
found help here after many hours of googling http://www.warsow.net/forum/viewtopic.php?id=9544
Props to fedora on core6 release, very impressed so far from a gentoo addict