Hi Shubhabrata, There's exist no such tool to convert ASP.NET application to a Silverlight application. ASP.NET applications & Silverlight applications are two different things and there is no relation between them. One is in .aspx and the other is in .xaml. The controls are all different for them. Thus, you can't use any tool to convert from one to another. If you want to migrate from one to the other, you have to know each technology first and then you have to manually convert them. Once migrated to Silverlight, you will get more power over your application with the help of Rich UI and StoryBoards.
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Regards - Kunal Chowdhury | Software Developer | Chennai | India | My Blog | My Tweets | Silverlight Tutorial