I have been using WS2K R2 in main primary laptop for last 5 months. I wanted to install the Windows Phone SDK on my server. Then I got the error that WP SDK is not compatible with the Server OS. I googled and finally found this useful link.
If you have an offine WP 7 installer like an ISO file extract them using any file compressing tool and follow the steps mentioned in the above link.
But another pain point is Zune does not support on the server OS. Don’t worry .. I did the search again found this following link.
Personally I didn’t check the Zune install on Windows Server 2008. So if it is not working don’t blame me, I just believe the Google 🙂