Try the command at the bottom of following link:

http://social.technet.microsoft.com/Forums/en-US/ocsplanningdeployment/thread/b566ec61-92ec-4187-9142-ec37e5a5d4e4

If you are trying to install Lync on DC, you will have error.

You might need to change the path to SQLEXPR_x64.exe...