From an article on ZDnet, it appears that Groove will be part of Office 12 in order to add much richer collaboration services to the next release of Office. This will include finding out if co-workers are online and available, then finding a way to share pre-determined data. This knowledge will include the IM services as well as Internet Telephony!
"The ability to handle voice over Internet Protocol technology is "one of the core features (Microsoft is) building into the next version of Office," said Hilf, Microsoft's director of platform technology strategy. The company also plans to continue adding more server-based productsto the Office family of products, he said."