Did you rehome it to your Exchange 2007 server?
To remove the public folder mailbox and stores, on the Exchange 2003 or Exchange 2000 server, use Exchange System Manager to perform the following steps:
- Expand the server, expand the storage group that contains the public folder store, right-click the public folder store, and then click
Delete.
- In the dialog box that notifies you that the public folder store is the default store for one or more mailbox stores or users, click
OK to select a new public folder store. In the Select Public Store dialog box, select a public folder store on an Exchange 2007 server, and then click
OK.
How to Remove the Last Legacy Exchange Server from an Organization
http://technet.microsoft.com/en-us/library/bb288905(EXCHG.80).aspx
James Chong MCITP | EA | EMA; MCSE | M+, S+ Security+, Project+, ITIL msexchangetips.blogspot.com