how to replace a widget or make an overlay?

[tom dbservice com]

I have a simple window with one treeview. When the app is shutting  
down it currently creates a popup with an icon and a few lines of  
text. Since these types of popups are annoying, I'd like to remove it  
and draw the stuff directly into the main window, into the center of  
the treeview. The treeview will be emptied when the stuff needs to be  
drawn, so the stuff will basically be on white background.

How would I go implementing it? Is it possible to replace the treeview  
and put a box there, with the same size, and the stuff in the center  
of it? Or is it possible to put the stuff over the treeview, kindof  
like an overlay?

thanks
tom