You could try this (Work on a copy!!)
Code:
Sub OnSlideShowPageChange(SW As SlideShowWindow)
Dim osld As Slide
If SW.View.CurrentShowPosition = 2 Then ' this is slide 2
Set osld = SW.View.Slide
osld.Shapes("ShockwaveFlash1").OLEFormat.Object.Playing = True
End If
End Sub