Could you explain the case in more details? From what I can gather you are having issues with passing the data to the server which is not a task related to the RadWindow control. Getting the object from the argument should not differ from the logic from this demo and should work fine both in the latest and in the Q1 2011 versions: http://demos.telerik.com/aspnet-ajax/window/examples/dialogreturnvalue/defaultcs.aspx
For your convenience I am adding here a simple page that shows one way data can be passed and edited like this. I hope you find it helpful.
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