I need a popup control or script that I will be able to place another control in and have the response sent back to a textbox on my asp.net page.

Here is the best I can say in plain english. I will have a button on my page (.aspx) that needs to open a popup with a treeview in it. Then have the selected item from the treeview populate a textbox on the page.

I assume the popup will need to be done via javascript, but I'm not sure how to get the contents back to the textbox.