Well, sometimes it takes a day or two...
Anyway, after removing your existing Omega or ATI driverset, can you manually install the Standard VGA driver by right clicking the desktop, clicking Properties, clicking the Settings tab, click Advanced, click the Adapter tab, click Properties, click Driver tab, then click Update Driver and follow that through? That should give you the basic driver foundation that the installer is looking for.
You may want to make use of the Search function here at DH to look for posts dealing with driver installation - there are likely hundreds if not thousands though - but reading some of those should give you a better idea of what to try to do that closely matches your circumstance.
Also, try this thread for a nice list of fixes and suggestions:
Common Problems and Fixes
and look at other posts in the Windows Radeon Display Drivers forum in addition to the posts in this forum - those posts will apply to your installation procedures as well...
Good luck, and welcome to DH. Feel free to post back with any result or other problem you may have...