Try another keyboard, just to be sure that this is the issue. If you can not interrupt the boot and go into Setup, then the problem is not in Windows configuration.
Will booting into safe mode (press F8 early in the boot process and select Safe Mode from the menu) help?
If the machine has a PS2 connector, borrow a PS2 keyboard to fix the problem.
Put the OS disc in the drive, boot to it, and try a Repair installation.
If none of these solve the problem, let us know what happens at each step and we can make more suggestions.