This is exactly the reason why a PC repair guy/gal always has a PS/2 keyboard on hand.
However, I recently bought a new ASUS mainboard (P5 series). After installation of the Express Gate software (came with the board) the boot sequence was altered. Instead of seeing the expected BIOS screen there is now a menu which allows me to boot the PC, connect to ASUS (internet), play music, play internet games. This whole menu is controlled by keyboard and mouse (both USB).
When I select the boot option the expected BIOS screen appears and it is business as usual.