Starting with RC0 and continuing through our RTW release of Silverlight 2 Tools for Visual Studio, we’ve moved the developer runtime installer into a downloadable dependency.  This makes the Silverlight Tools chain installer smaller to download, but causes the install to always download the installer for the development runtime.  We chose this method mainly so that any updates to the runtime will still work with the same Silverlight Tools installer.  The drawback is that you have to have an Internet connection in order to install.  But there’s a solution…

The installer package we use, which is the same as for Visual Studio 2008 SP1, has a flag which will download all of the required dependencies into a specified folder, containing an offline-installable set of packages.  To do this, you simply need to run the chain installer (from a computer with an Internet connection) as follows:  Silverlight_Tools.exe /createlayout <Full path to output folder, e.g. C:\foo>

After the installer finishes, you’ll find in the specified path (C:\foo in my example) that all of the contents have been downloaded and extracted, including the Silverlight 2 development runtime.  You can copy this folder to any other machine and run SPInstaller.exe and it will no longer need to download the runtime.

[Update:]

Here is an alternative way to create an offline installable layout, in case the above doesn’t work (e.g. due to proxy issues).  If you run the installer with the /x flag, it will extract the contents to a specified directory: Silverlight_Tools.exe /x:C:\foo

At this point, you can download the developer runtime separately (see http://www.microsoft.com/silverlight/resources/tools.aspx for a link to the developer runtime) and copy it to this folder.  Then run SPInstaller.exe as above.