You'll want to create a linked mailbox.
http://technet.microsoft.com/en-us/library/bb123524.aspx
Mark
Mark E. Smith | Capax Global Consulting
MCA: Exchange 2010 (Ranger) | MCM: Exchange 2010
MCTS: Virtualization, OCS, SCVMM, SCOM, MOSS, ISA
http://marksmith.netrends.com