Hi Milos,
If you're integrating by way of the Cisco UC Integration for Microsoft Office Communicator, you only need the standard CAL as yes, CUCM will take care of the call control.
Regarding Windows 7 and 64 bit, we will be supporting Windows 7 in our 8.0 release of the Cisco UC Integration for Microsoft Office Communicator which will be available Q2 of 2010. It will be a 32 bit application that can run on Windows 7 in 32 bit emulation (WOW64).
Heather
Product Manager
Cisco Unified Communications