Microsoft Office Communicator 2007 is the replacement for Office Communicator 2005 that runs on Windows Vista, XP or 2000 SP4, and includes a new look and crossoperator compatibility as part of the alliance between Microsoft and Nortel.
This alliance ( called the Innovative Communication Alliance) brings new interesting features for a corporate environment, for example:
VoIP Calls (compatibility with Nortel Hardware)
Call Conference between multiple IM contacts
Call Fowarding and Redirect to Voice Mail
Start Call From Email Link (integration with Outlook 2007)
Add users from Outlook Contacts (Integration with Outlook and Vista Contacts)
Integration with Office Live Meeting 2007
Enhanced privacy control
Rich Text Formatting for IM Chat
Integration with One Note
Calls and Chat History
The first thing you will notice is the new look, also on the server side are new benefits but since you only access the client you won't notice it. The system requirements are the same and opposite to previous consumer IM clients from Microsoft, Office Communicator 2007 performance is still the same that 2005.