I am trying to create a map which will include radar rainfall data in a KML format. How can I easily do this using the Silverlight API (the version doesn't matter)?
KML layers are not natively supported in AGS web APIs, AFAIK. There is a code sample that you can get inspiration from in the Resource Center: http://resources.esri.com/arcgisserver/apis/silverlight/index.cfm?fa=codeGalleryDetails&scriptID=16487
A KmlLayer class has been added at to the Toolkit at version 2.1, which is currently in beta.