maxgui best way to do a processing msg

I want something simple i can do:

messagebox("waiting for renderer...")

This then stays on the screen during processing something done by an external app.
I know i can do it with a new window but i dont want that, I would like a box in the center of my existing main window which is on top of all other panels etc.

Create a window and deactivate everything else until the app finishes?

See disabling example given here:
http://www.blitzbasic.com/Community/posts.php?topic=63641

P.S.: Wrong forum! ;)