Outlook 2000 and earlier versions put all messages, attachments, contact lists, the calendar, etc. in one file. There are advantages and disadvantages to that approach. But Microsoft's Outlook developers coded the software in such a way that when that file size nears 2 GigaBytes (GB), the file becomes corrupt. And Outlook provides no forewarning that one is nearing the 2 GB limit. Once you reach about 1.96 GB the file becomes corrupted and you may not even be able to start Outlook.
Microsoft's Inbox Repair Tool, scanpst.exe, can't repair the damage. The only repair mechanism Microsoft provides is the Oversize PST Recovery Tool, PST2GB. That tool will arbitrarily truncate the PST file to less than 2 GB, which then allows it to be repaired with the Inbox Recovery Tool. However, you have no control over what data is removed by the truncation process, so some messages will be lost.
For instructions on how to repair a file that has reached the limit, see Repairing Outlook PST File Corruption at 2 GB Limit