[rhn-users] display failure after exceeding 256 colors with radeon 7500

[Jason M Hurst Frye]

Heya.. 
I am running RHEL WS.  After installing and updating, I tried to adjust my display settings higher than 256 colors.  In previous installation attempts I have this same problem - I reboot to a blank screen (my moniotor shuts off).  I was hoping that after the updates, I wouldn't have this problem, but here I am again.
I would like to know 2 tihngs if possible...
1) how can I edit my etc/X11/XF86Config file or replace it with the etc/X11/XF86Config.backup file?  what steps do I need to take to get to the nessesary prompt? (through GRUB?)
2) What do i need to do to enable more than 256 colors without rendering my system unusable?

specs:
AMD Athalon XP 1.8 gig 
Radeon 7500 (detected on install)
17" Relisys monitor (detected on install)
1 gig DDR RAM
MSI K7N2G w/ nForce2 chipset (motherboard)
WD 80 gig  hard drive