we have a user that was created in abc domain and they have since moved to a different department and now belong to xyz domain.  they still have the same logon creds as abc domain but the email box is associated with xyz domain.  i am having a issue getting author permissions on public exchange folders.  any suggestions?  can i delete the AD account in xyz, have an orphan email account and attach it to the abc domain name?

What are these domains you're talking about?  AD logon domains? Email domains?

Exchange 5.5 is largely ambivalent about the logon domain, especially when it comes to Public Folder access - PF access is controlled exclusively through the Client Permissions button on the Properties of the PF.

Access to a mailbox is controlled by the Permissions tab of the mailbox, where you specify which NT or AD accounts can access the mailbox and what level of access they're allowed.  BTW, if you can't see the Permissions tab on objects, there's an Option you can set in Admin to show it for all objects.