Hello Bob
I was able to create more than 3 tabs by:
1) Adding more layers to the dialog.  With dialog showing, select "Edit / Layers" from top menu bar.  Add as many layers as you wish to have buttons for.
2) With tab selection on the dialog.  Copy and paste one of the tab buttons, add as many as you need.
3) Modify the code associated with each NEW button.  See the code below, it was modified for adding a  4th button.
Sub Layer4_EventClick()
Dim This : Set This = Layer4
	This.ButtonShape = 2
	LayerOneButton.ButtonShape = 1
	LayerTwoButton.ButtonShape = 1
	Dialog.Layers("Layer1") = False
	Dialog.Layers("Layer2") = False
	Dialog.Layers("Layer3") = False
	Dialog.Layers("Layer4") = True
	This.BackColor = vbWhite
	LayerOneButton.BackColor = -1
	LayerTwoButton.BackColor = -1
	LayerThreeButton.BackColor = -1
End Sub 
Hope this helps
TomF