problem with outlook 2000 / exchange 5.5

One of the computers in our office is running Outlook 2000 and all of the messages that come into the "inbox" mysteriously dissappear after a short while. I have done virus scan and none were detected even with the latest definitions updates... I am not sure if this is a client problem because the same thing was happenning with Outlook 98; that is why I put 2000 on the computer, and removed 98.

I was wondering if there are any settings in Outlook that automatically process mail, etc... I checked for any VBA scripts/macros or "rules" and none were listed as being used.

I know I had the same problem with a different computer running Outlook 97 and I uncheched the "automatic processing" option and the problem stopped... But who knows, maybe it was coincidental.

Also, could there be something going on with the exchange server so that it is losing mail? System-wide, everything is fine, it is only this one computer that seems to do it...

Please help!