You need to switch to runlevel 3 (a non-graphical-login runlevel) so init won't keep respawning gdm (or xdm or whatever Redhat uses for a graphical login these days)...
Switch to a text console (CTRL-ATL-F1), log in as root, and type 'telinit 3'. You'll probably see it shut down a couple of services, and your graphical login will go away. You should be set to install the driver or whatever else you want to do. To go back to runlevel 5, type 'telinit 5'.
In case you're curious about runlevels and init, take a look at /etc/inittab, or the manpages for init and inittab.