I recently needed to install the SilverLight 3 Visual Studio Tools in a VPC that was not connected to the internet.  Unfortunately, the installer wants to connect to the internet to download the SilverLight SDK and won't complete without a connection.  I know I could reconfigure the network settings on the VPC to connect to the internet, but I have it configured for a special project and I had spent hours getting things just right and didn't want to mess it up.  I eventually found this workaround on the internet:

• Download the SilverLight tools for Visual Studio
• Download the SilverLight SDK
• Copy these files over to your VPC and put them in the same directory
• Extract the contents of both of these setup files into the same folder by running both insallers from the command line with a /x parameter at the end
• In the extracted files, run vs_silverlighttools_setup.exe

It will take a few minutes, but this will install the tools without connecting to the internet.

http://blogs.msdn.com/jamlew/archive/2009/03/24/understanding-issues-installing-silverlight-3-via-web-platform-installer.aspx