The NGO guys have posted a quick summary & six links to forum threads about the black screen issues that many users are experiencing while using a 7800GS AGP. Seems that even though the NGO optimized driver seems to fix the issue, neither of the affected board manufacturers (XFX & eVGA) are interested in pursuing that avenue as a solution.

"The most affected hardware is on the EVGA and XFX boards. Both firms have confirmed these issues and EVGA has even offered a beta BIOS as a workaround."