I only installed Linux for the first time a few weeks ago, so take this with as many grains of salt as you wish...
What worked for me - after installing the driver and making the changes to the xfree86 file, reboot and enter your BIOS settings. There are 2 video settings you'll want to change: 1 - Plug N Play OS? needs to be N, and 2 - Allocate IRQ to PCI VGA needs to be Y. (I'm at work now, so my apologies if I got the names wrong). After doing that, I was able to start X with no problems.
Additional note - I'm dual-booting RedHat and Windows XP, and although making those changes fixed my Linux video problems, XP wouldn't boot back up until I changed them back.
<shrug> Whatever that's worth.