这是Silverlight4_Tools下载，如果遇到VS2010无法调试Silverlight应用的话，到控制面板-添加删除程序中，找到Silverlight，然后卸载删除后，下载该Silverlight4_Tools.exe重新安装即可调试。
This package is an add-on for Visual Studio 2010 Beta 2 to provide tooling for Microsoft Silverlight 4 and RIA Services. It can be installed on top of either Visual Studio 2010 Beta 2 or Visual Web Developer 2010 Express Beta 2. It extends existing Silveright 3 features and multitargeting capabilities in Visual Studio 2010 to also create applications for Silverlight 4 using C# or Visual Basic.
•Support for targeting Silverlight 4 in the Silverlight designer and project system
•RIA Services application templates and libraries
•Support for Silverlight 4 elevated trust applications and other new Silverlight 4 features
This download will install all components necessary for Silverlight 4 and RIA Services development:
•Silverlight 4 developer runtime Beta
•Silverlight 4 SDK (software development kit) Beta
•Update for Visual Studio 2010 Beta 2 and Visual Web Developer Express 2010 Beta 2 (KB976272)
•Silverlight 4 Tools for Visual Studio 2010 Beta 2
•WCF RIA Services for Silverlight 4 Preview
1、从微软的网站下载Silverlight4_Tools.exe）
2、执行Silverlight4_Tools.exe
3、像Silverlight3_Tools一样，Silverlight4_Tools还是会在线下载Silverlight_Developer.exe。
4、将Silverlight4_Tools.exe的文件名改为Silverlight4_Tools.exe.zip
5、解压缩Silverlight4_Tools.exe.zip
6、解压缩后可以看到一些安装文件。依次按照下面的顺序执行安装程序，前三步的文件都可以在解压缩的目录下找到。
1）VS10-KB982218-v4.exe
2）silverlight_sdk.msi
3）VS_SilverlightTools_Setup.exe
4）Silverlight_Developer.exe
8、一切OK
