I think changing the default template will not be enough to achieve the look and the behavior of the control you describe with the picture. I guess you will need to add string paths to specific files in the TextBox
and so on. But, this cannot be achieved in Silverlight due to security restrictions. The way to chose file is via OpenFileDialog used internally in the RadUpload.
On the other hand, have you considered using a custom control which can use RadUpload programmatically instead of re-designing the default template?
All the best,
the Telerik team