cat /etc/X11/xorg.conf
If you are using the binary nvidia driver, this will have entries in it. It will be empty otherwise. Dunno how to force nv or vesa though - without writing a device section.
I guess you can look in lsmod
lsmod | grep vesa
lsmod | grep nv
looking in the xorg log files will tell you, and the syslog too.
It may just be a matter of something like
#yum install kmod-nvidia
http://www.mjmwired.net
... look for the f12 notes.
note: Fedora Core is no more after FC6. After that it is just fedora (note, lower case f).