I tried out this code, it adds a pushpin to the map (objMap) when you click the left and right mouse buttons together (all you have to do is change the Button value to switch)
Code:
Private Sub objMap_BeforeClick(ByVal Button As Long, ByVal Shift As Long, ByVal X As Long, ByVal Y As Long, Cancel As Boolean)
If Button = 3 Then
Dim pinLoc As Mappoint.Location
Set pinLoc = objMap.XYToLocation(X, Y)
objMap.AddPushpin pinLoc, "great"
pinLoc.goto
End If
End Sub
Hope this helps you