WORK-A-ROUND
I have had the same issue with popup and dialog forms in 2007. They work Ok for a while but then go to miniscule, especially when porting to another computer.

My work-a-round which is working so far is to re-sze them on load, setting the InsideWidth and InsideHeight attributes eg

Private Sub Form_Load()
Me.InsideWidth = 4300
Me.InsideHeight = 8000
End Sub

...