TechContrarian

You Can Download Microsoft Office Communicator Mobile 2007 R2 from the following Link – http://www.microsoft.com/downloads/details.aspx?familyid=BC08CDB7-98E9-47E5-AA63-EB17C2CE4592&displaylang=en (CommunicatorMobile.PPC.msi) or
http://www.microsoft.com/downloads/details.aspx?familyid=93062936-F216-4D97-AA13-105A20454322&displaylang=en (CommunicatorMobile.SP.msi Form Link)
As per the Article (Installing Communicator Mobile for Windows Mobile from a Storage Card Link http://technet.microsoft.com/en-us/library/dd425083(office.13).aspx) you need to have a .CAB file, by default only .MSI is downloadable from the Microsoft Website.
You can install the Communicator Client via ActiveSync Installing Communicator Mobile Using ActiveSync 4.5 Ref Link http://technet.microsoft.com/en-us/library/dd425350(office.13).aspx. You can use CommunicatorMobile.MSI file to install CommunicatorMobile on the Windows Mobile.
However if you would Try to install ActiveSync on the Vista Machine you will getting following error:

 
The only option you are left with is to install the CommunicatorMobile via Cab file. Since there is no direct .cab download for CommunicatorMobile following is the workaround.
Workaround
1.    Create a Folder name COMO on the C:\ Drive
2.    Download .MSI in the COMO Folder.
3.    Open Command Prompt, and Change folder to C:\Como.
4.    Run [...]