Microsoft has released Silverlight 5 Tools for Visual Studio 2010 SP1

This package is an add-on for Visual Studio 2010 SP1 to provide tooling for Microsoft Silverlight 5 and Microsoft WCF RIA Services V1.0 SP2 . It can be installed on top of either Visual Studio 2010 SP1 or Visual Web Developer 2010 Express Service Pack 1. It extends existing Microsoft Silverlight 4 features and multitargeting capabilities in Visual Studio 2010 SP1 to also create applications for Microsoft Silverlight 5 using C# or Visual Basic.

This download will install all components necessary for Microsoft Silverlight 5 and Microsoft WCF RIA Services V1.0 SP2 development:

Silverlight 5 Developer Runtime
Silverlight 5 SDK (software development kit)
Update for Visual Studio 2010 Service Pack 1 and Visual Web Developer Express 2010 Service Pack 1 (KB2502836)
Microsoft WCF RIA Services V1.0 SP2

  Silverlight 5 Tools for Visual Studio 2010 SP1