When you initially disable an Exchange 2007 mailbox it normally does not become visible in the EMC until after the administrative tasks have run overnight. You can speed this process up using the Clean-MailboxDatabase commandlet e.g.
C:>Clean-MailboxDatabase -Identity ex2k7-virt-1\v1sg1\v1sg1db
It may take a minute or two to appear in the disconnected mailbox list.