Actually I'm not so sure bout this.
I used to get same prob with ATI 9800 - screen black, game continues for about 30 secs then crashes back to BIOS.
Took a screenie of an error message one time which showed game was attempting to write to the AGP/PCI bus restricted memory space.
Using omega drivers can be fixed by using program files/advanced smartgart options and turning OFF AGP writes, leave reads ON.
These are only for error checking anyway.
Since doing this I have not had one black screen.