In this short post I will show you how to add the xap file in ClientBin folder when you add silverlight project to existing web project. Right click on the web project and click on the properties option from the menu. After clicking on the properties window click on the "Silverlight Application" option you will see window as shown in Image 1.
Click the add button you will see the window as shown in the Image 2. From here you can see the silverlight project options in the comboBox as shown in the Image 2. you can select any project you want to include in the web application.
Hope you get idea of how to include the xap file in the web application when you add the silverlight application to your existing web applications.All and any comments / bugs / suggestions are welcomed!