Make sure your motherboard drivers are as up to date as possible, particularly the AGP port one, also check the AGP Aperture, it should be set quite high, 128 to 256 Mb.
As for drivers:
As I recall Omega drivers are modified by helpful programmers who 'tweak' official releases, sometimes adding or unlocking features left out or locked by the official programmers.
First is to install the drivers that came on the card install CD, if they work my advice is to leave well alone, AGP driver support is not exactly strong.
Try looking to the Gigabyte site, they may have updated drivers, those on the install CD will be at least weeks, if not months old, an age in computer terms.
Next port of call is the ATI site.
If that fails, check out Driverheaven, they have a comprehensive archive.