If you are installing the collaboration service on the same machine as the BES, then you would need to "re-install" the BES. No, worries there. Just start the setup program again, choose BES from your left list and LCS/Office Communicator from the list on the right, and then use all the default settings and the same database and you should be ok.
Stupid I know.
PS: You havent already done that have you?