Si no recuerdo  mal, para averiguar los twips por pixel había que llamar a
una API. ¿La tenéis a mano?

RESPONDE HAPPY
==============

'Authors:     Stephen Lebans
'                  Terry Kreft
'Date:         Dec 14, 1999

' Create an Information Context
 Declare Function apiCreateIC Lib "gdi32" Alias "CreateICA" _
  (ByVal lpDriverName As String, ByVal lpDeviceName As String, _
  ByVal lpOutput As String, lpInitData As Any) As Long

' Close an existing Device Context (or information context)
 Declare Function apiDeleteDC Lib "gdi32" Alias "DeleteDC" _
  (ByVal hDC As Long) As Long

 Declare Function GetDeviceCaps Lib "gdi32" _
 (ByVal hDC As Long, ByVal nIndex As Long) As Long

 Const LOGPIXELSX = 88

Function GetTwipsPerPixel() As Integer
' Determine how many Twips make up 1 Pixel
' based on current screen resolution

Dim lngIC As Long

  lngIC = apiCreateIC("DISPLAY", vbNullString, _
  vbNullString, vbNullString)

  ' If the call to CreateIC didn't fail, then get the info.
  If lngIC > 0 Then
    GetTwipsPerPixel = GetDeviceCaps(lngIC, LOGPIXELSX)
    ' Release the information context.
    apiDeleteDC lngIC
  Else
    ' Something has gone wrong. Assume a standard value.
    GetTwipsPerPixel = 120
  End If

End Function