The file you need to back up is your Personal Folders file (*.pst) It's
where all the mail, calendar, contacts etc are stored.
Take a look at these pages for info on Outlook data backup:
http://www.slipstick.com/config/backup.htm
http://www.howto-outlook.com/Howto/backupandrestore.htm

Signature
Russ Valentine
[MVP-Outlook]
>I need to reformat my hard disk urgently, and have completely forgotton how
> to make a copy of my contacts and Calendar.
> Urgent help needed, please
> Thanks