MS Exchnage 5.5 mailbox issues.

I am currently working as a LAN administrator on a Windows 2000 network running Exchange 5.5 (Ya I know we need to upgrade but the people who sign the checks like it the way it is). Anyways a user was having difficulties opening up outlook to access thier mailbox. The prior day they had no issues but today it wouldn't open, when it crashed it would reboot in safe mode and just keep crashing. A coworker (who is a domain administrator) of mine went into Active Directory and gave themselves permissions full mailbox access to the user's mailbox. When they tried to open outlook to try and recover the emails outlook crashed at the same point that it did for the user. So my coworker thought it would be a smart move to go into the exchange tasks of AD and remove the exchange attributes then creat a new mailbox. Problem solved right? No because now my boss wants me to get the emails from the old mailbox, put them in a pst, and then attach the pst to the new email account. The old mailbox is still showing up in the exchnage system manager but I have no idea how to access it since it's no longer attached to the account in AD. Any and all assistance is greatly appreciated, thanks in advance.