Hi Scott -
Store.exe is the Exchange 2000 information store process. The information store houses the mailboxes for your Unity subscribers. Since this is an on-box Exchange environment, I would contact Cisco TAC. Let them know if you are seeing any errors in the application or system event logs. Run the GUSI tool from the Unity Tools Depot, which will provide Cisco the Exchange service pack level and other pertinent information.
Ginger