OK, I know that it has been a long-time discussion about the Process Order button getting clicked multiple times, and the difficulty in "turning off" a button... BUT..... here's a thought.
(Pseudo-Code follows)
<div ID="PreButtonPush"><img src="ClickToProcessOrder.gif"></div><div ID="PostButtonPush" visible="false"><img src="Processing.gif"></div>
' Button pushed
PreButtonPush.Visible = False
PostButtonPush.Visible = True
... so just hide the one button, and unhide the graphic, when the button is pushed.
Can that be done easily?