I assume you installed OfficeXP over Office2000?
Did all of your folders and other settings migrate over to the new version? I am guessing they didn't. If this is the case, find out where your outlook.pst folder is on your hard drive. Mine is in c:\Documents and Settings\username\Local Settings\Application Data\Microsoft\Outlook.
Open Outlook, go to \File\Open\Outlook Data File and choose your outlook.pst wherever you found it.
If I guessed right, its all right here and nothing lost. I do an export of all my Outlook folders into a backup.pst file ever so often and ALWAYS before reinstalling my OS and Outlook. Then you can just import it into your program when you start it up again.