MS Exchange 2000 Mailbox Size

Hi guys I have MS Exchange 2000 running on MS Windows 2003 Server. My question is I have 2 users in the Server Manager showing the incorrect size of space they are using. One of them shows it is using around 600MB, but when I login as the user thru MS Outlook 2000 and check on the size, it shows that it is using around 180MB of the total size for all the items. Including calendar, inbox,deleted items,sent items,etc…Help please…Thanks all.