Exchange 2K Query

Does anyone know of any product that will allow deep traverse searching of the MAPI public folder store in Exchange 2000? I need to set up a system whereby all users working on a project can drop their email into the relevent area in a public foldertree. The resulting tree must be searchable. Alternatively I might set up a project mailbox, and allow all users access to this mailbox. Is there a realistic limit on the size of a mailbox or the amount of users that can connect to a mailbox. The mailbox will be used by about 100 users, and could grow in size to about 5GB.

Any help appreciated.

Cheers,

Damian