Thanks to everyone who responded. fireberd
nailed it: I had to reinstall Office 2003 in its entirety before Outlook would work.
Now I face another problem. Sigh.
Outlook 2003 cannot, as far as I can make out, import mail settings and the mail itself from Windows Live Mail.I'm doing a search on the Microsoft site for a solution and if I can't find one I'll be right back here pleading with you nice folks for help again.