Outlook uses all disk space then…

I have one computer with a Microsoft Outlook problem. When the user opens Outlook, the program title screen stays on desktop while all the hard disk space (about 500 MB) dissapears tnen crashes stating that there is no more hard disk space available. I tried scanning for a virus, uninstalling and reinstalling Outlook 2000, upgrading to Outlook 2002 and nothing changes. Has anyone else experianced this? and do you have a solution? Thanks