Windows On Mac :: Possibly Fatal Boot Camp Error / Unable To Boot Windows

In my attempt to install Windows XP via Boot Camp, I accidentally inserted an SP1 disc instead of the SP2 disc that I have. The installation proceeded to the point where it does for most who attempt this: the screen where you are prompted to press ENTER. I could not proceed and therefore restarted the iMac and held down the mouse button upon start-up to remove the CD.

HERE IS THE PROBLEM:I can not boot into OS X because the keyboard shortcuts (those that might allow me to select which partition to boot from and/or reset PRAM) seem to be disabled. Instead, a reboot always ends at a black screen with a blinking DOS-esque cursor, or the prompt: "No bootable device -- insert boot disk and press any key."

I have attempted inserting my SP2 disc at this point, to no avail. My keyboard seems to be disabled, as if the SP1 install proceeded just enough to establish itself as the boot drive without drivers for the keyboard. I've tried using all 3 USB ports, disconnecting other USB devices. Oddly, my bluetooth mouse works to eject the CD on reboot...