The drivers can be downloaded from here
Reboot and at the GRUB screen hit "e". You should see something like...
kernel /vmlinuz ro root=/dev/hdc5
On the line "kernel" line add the number 1 (one) or 3 (three) at the end similar to...
kernel /vmlinuz ro root=/dev/hdc5 1
This will boot you into run level 1 (super user mode) or 3 which is text mode. Eventually you will see a prompt
navigate to the directory where the dowmloaded file is and install with
rpm -ivh ati-x11-drv-------.rpm
(there may be dependency issues so yum install ati-----.rpm may be better)