Silverlight 4 Tools Installation

For some reason, I have to run SL 4 projects. However, I receive a ton of compiling errors. Then I tried to re-install all of the SW needed for SL API project by referring to http://help.arcgis.com/en/webapi/sil...0000005000000/.
I repaired VS 2010 and VS 2010 SP1. Then I tried to install Silverlight 4 Tools for Visual Studio but got failure. The error message is:
Installation Requirements:
Visual Studio 2010 or Visual Web Developer Express 2010 or Visual Phone Developer Express 2010 that matches the language version of Silverlight Tools 4 must be installed before installation of Silverlight Tools can continue. Silverlight Tools is available in other languages at <a href="http://go.microsoft.com/fwlink/?LinkId=177432">http://go.microsoft.com/fwlink/?LinkId=177432">http://go.microsoft.com/fwlink/?LinkId=177432">http://go.microsoft.com/fwlink/?LinkId=177432</a>[<a href="http://go.microsoft.com/fwlink/?LinkId=177432">http://go.microsoft.com/fwlink/?LinkId=177432" target="_blank" title="New Window">^</a>].
Since I did have installed VS 2010, I don't know what measure I should take next.  Thanks.
By the way, got another Q here. From the API:
Silverlight Version 4 is supported:
Silverlight 4 Tools for Visual Studio (add-on required if using Visual Studio 2010 without SP1)
Since I installed SP1, is the SL 4 Tools still required?