Silverlight is a powerful tool we can use to develop rich cross-browser applications. Silverlight supports most of the popular browsers and it can run on different devices as well. Microsoft CRM 2011 provides OOB support for Silverlight web resources. We can develop a Silverlight web application in Visual Studio having Silverlight tools installed and can deploy it as a Silverlight web resource in Microsoft CRM 2011. We also need to install Silverlight developer runtime if we want to debug our Silverlight application.
You can download Silverlight runtime from http://www.silverlight.net/downloads.