OK so i have a hack that is close. Please let me know if there are other things I may need to consider as I may not understand everything that is going on under the covers with the RadWindow.
It looks as if the parent to the RadWindow is actually a Window which is accessible after the RadWindow has loaded. If you are attempting to use the RadWindow for the MainWindow of your WPF application it is possible to get the RadWindow to show up in the taskbar as follows.
In a Loaded event handler for the RadWindow you can do something like the following...
| if (this.Parent is Window)
| Window thisWindow = this.Parent as Window;
| thisWindow.ShowInTaskbar = true;
| thisWindow.Title = this.Header.ToString();
The above code does get the RadWindow to show up in the taskbar and at first glance it does seem to behave properly. Please let me know what other considerations there are here.