RadWindow for ASP.NET AJAX is the successor of RadWindow of ASP.NET. It
is part of the RadControls for ASP.NET AJAX suite and the new line of products offers much
more stability and new functionality.
It is a prerequisite to have ASP.NET AJAX installed when using Telerik RadControls for ASP.NET AJAX.
More information on the subject is available in the FAQs
and in the documentation
the Telerik team