Are you connected toa PST?
Maybe a server side rule that is being applied but stupid Outlook isn't displaying it correctly. Try connecting from another machine and see if that helps.
Preferrably somewhere your profile doesn't exist yet.
Can you see exchange admin?
I'm not familiar with Exchange 2000, but in Exchange 5.5 you can see howmany items are in your mailbox total. Check it before you move, and after.
Also try
http://housecall.antivirus.com/ house call, its a free online virus scanner
or maybe install
AVG free antivirus software.