I just wanted to clarify that we are NOT supporting SSMS 2008 Express. We can prevent SQL Source Control from loading in SSMS 2005 Express, but we can NOT prevent it in 2008 Express.
It may work, but unfortunately, if there are any issues we will NOT be able to support them at this time.
The supported versions can be found on our website at http://www.red-gate.com/Products/SQL_Source_Control
and then select "Requirements and prerequisites" on the right.
Stephanie M. Herr
SQL Source Control - Project Manager