Window Messages for PPT 2007?

Can anyone point me towards documentation (or even just a header file)
for PowerPoint 2007 window messages?

I am trying to figure out a program that appears to be sending a
WM_USER+22 (0x0416) message to a powerpoint slideshow to advance the
show. But that approach doesn't seem to be able to "interrupt" an in-
progress animation; e.g. the show doesn't advance until the animation
is finished, even though a mouse-click within the same powerpoint show
would advance immediately.

I'm mostly interested in finding the closest possible alternative
message to use instead of WM_USER+22...