Here is an article that explains the use of the window.dialogArguments method. In the article is even an example that combines that property with the window.showModalDialog method.
The article: http://msdn2.microsoft.com/en-us/library/ms533723.aspx
Caution: You have to remember that those methods of the window class are case sensitive. window.showmodaldialog is not the same as window.showModalDialog !
Hope this helps!
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