You should be able to do a lot of things to get the driver updated:
1) in grub edit the startup line and set the run level to 3 (pick the first option, edit the second line and add a 3 to the end (freestanding)). boot. install your driver (download it via links if you can't get it down onto a usb stick). (this change is transient and you have to do it everytime you want to boot to runlevel 3 ... know how to do this and you can boot to runlevel 1 and recover your root password
)
2) when you get your X thingo hit CTRL + ALT + F1 and install your new driver. (may work). reboot ... (or restart X an alternate way).
One comment, on my work laptop FC4 had the bad habbit that it did the same thing, the way to fix it the best way (in the short term) was to flick the system to the external display and back and after that it would work. I never bothered to resolve it ... my proper workstation arrived ... and later installs of FC did not have this issue. (I'll try to install FC6 on that today come to think of it)...
good luck
