You have a couple of choices *if* the computer is still up and
running.
Belarc Advisor (downloaded, installed and ran) on your PC with Office
2003 should reveal the CD Key to you.
http://www.belarc.com/
Magical Jelly Bean Keyfinder v1.5B3 (downloaded, extracted and ran)
on your PC should also reveal this key.
http://www.magicaljellybean.com/keyfinder.shtml
Please notice that the version of the Magical Jelly Bean Keyfinder is
the BETA version, not the last full release. It is actually found
here:
http://www.magicaljellybean.com/kfbeta.shtml