WINDOWS XP - USB

Help, I'm using winxp pro on my ADM-1800+ computer. While using my
computer last night I accidentally deleted some drivers that caused my
computer to constantly reboot. I think this is an easy fix, I've been
trying to repair my OS. However, I've been using a USB keyboard and
when my computer reboots all I can access is my BIOS, and my keyboard
doesn't respond in windows to order my system to boot off of my CD-ROM.
It seems like windows has disabled my USB keyboard, causing my computer
to constantly reboot. Also, it appears to be that the BIOS version of
my motherboard (MSI-K7N420 Pro) is out-dated and doesn't allow me to
enable USB Keyboard in the BIOS and because windows disables PS2
connectors for keyboards when you use USB, I can't do anything to
select safemode, or anything. Please assist. I would like to know what
I can do to make this work. Do you recommend a BIOS update and is this
easy, and will it work without me being able to access windows.