I didn't see any BIOS options about AGP beyond aperture size or something like that.

The video card I want to use is a GeForge4 Ti4200, which, I think, means it's either 4x or 8x. The mobo manual claims it can deal with 1x, 4x, or 8x, as long as it's at 0.8V or 1.5V and not 3.3V. It also claims that 3.3V AGP cards are keyed differently, and mine definitely fits, so that's not it, I think.

You mean that F6 you've gotta hit if you want to install SCSI or RAID drivers? I might be able to install SATA driver there? I'll give it a shot.