In an effort to run Battlefield 2 on a radeon 9200 graphics card, I tried to change my BIOS settings.
I switched my primary video adapter from PCI to AGP/Onboard.
when I booted, my desktop is shifted to the left, offscreen, there's a funny border, and programs open far to the left, offscreen. when I try to access BIOS, all I get is a blank screen and a whirring hard drive.

how can I change my settings back?

(note: running battlefield is no longer a concern, I'm just trying to get my pc back to normal)

If you are saying you can no longer enter the BIOS Setup then you need to clear your CMOS.

Doing this depends on the motherboard. In some cases just removing the battery for a few minutes will do this. Some boards also have a jumper to clear.

If you can still access Windows you might have other options.

I switched my primary video adapter from PCI to AGP/Onboard.

Do you mean PCI_E?

If so why did you think changing to AGP/Onboard would help?

Anyway if you are shut out of the BIOS Setup then clear the CMOS.

Otherwise reloading your graphics drivers would be in order.