I ran into some Silverlight install problems on one of my computers. The Silverlight runtime installed fine. The SDK installer and the modifications to Visual Studio 2008 was where I ran into trouble.
Here are two blog posts that I found useful in solving these problems.
“Could not load type. Microsoft.VisualStudio.Web.Silverlight.IVsSilverlightService”
“The project type is not supported by this installation”