As related in my previous post, as I could not add the SQL Management Studio from SQLManagementStudio_x86_ENU I decided to try the next one on line,

SQLEXPRADV_x86_ENU.exe (502.7 MB)

It looks like the Add features to an existing instance of SQL Server 2008 brings up a window where everything is greyed out even in this version.

I decided to install with the other option,

P

erform a new installation of SQL Server 2008

This adds a new named instance of SQL Server Express which you will configure in the the SQL Server2008 Setup screens.

I have a default instance installed when I installed VS2010 and the new named instance (which I called VistaExpress) of SQL Express. Now both these can be accessed by the SQL Server Management Studio.

Bottom line:
If you already have a SQL Express installed by VS2010 then you can install SQL Server Managment Studio only if you install another instance.

Perhaps even SQLManagementStudio_x86_ENU can add in SQL Server Management Studio if you were to choose the first option (Perform a new installation of SQL Server 2008)