To develop Silverlight 4 applications you should first download and install Visual Studio 2010 or download and install the free Visual Web Developer 2010 Express edition.

Then install the Silverlight Tools RC2 for Visual Studio 2010.  This setup includes the Silverlight 4 Developer Runtime, Silverlight 4 SDK, RIA Services, and VS 2010 tools support.  Once installed you can do File->New Project and choose Silverlight Application to create your first Silverlight 4 project.  You can then use the new WYSIWYG Silverlight designer in Visual Studio 2010 to design and build rich Silverlight 4 applications.

Important: If you previously installed the Silverlight 4 Beta or RC build on your machine, please make sure to go into Add/Remove programs and uninstall the “Update for Visual Studio 2010 (KB976272)” package prior to installing the Silverlight Tools RC2 for Visual Studio 2010 setup. 

Note that while Silverlight 4 is released, the “Silverlight 4 Tools for VS 2010” is currently in “RC2” mode (meaning we are going to keep an eye out for any remaining issues before finally calling it done).  We’ll update the tools to be “final” in a few weeks once we verify that no last minute issues/bugs remain.