see the problem is that red hat doesn't have the driver for your card.
i don't know much about enterprise since most people just download the free version.
you could go to
www.ati.com and fount driver 3.7.0 for linux.
you should login in text mode, then install the package by using "rpm -Uvh <packakge's name>"
For XFree86 version use "rpm -q XFree86" to see what you have.
However i want to ask you why did you why enterprise?
are u using it to do business stuff?