Private Const CCDEVICENAME = 32
Private Const CCFORMNAME = 32
Private Const DM_PIXELSWIDTH = &H80000
Private Const DM_PIXELSHEIGHT = &H100000
Private Const CDS_TEST = &H4
 
Private Type DevMode
    dmDeviceName As String * CCDEVICENAME
    dmSpecVersion As Integer 
    dmDriverVersion As Integer 
    dmSize As Integer 
    dmDriverExtra As Integer 
    dmFields As Long 
    dmOrientation As Integer 
    dmPaperSize As Integer 
    dmPaperLength As Integer 
    dmPaperWidth As Integer 
    dmScale As Integer 
    dmCopies As Integer 
    dmDefaultSource As Integer 
    dmPrintQuality As Integer 
    dmColor As Integer 
    dmDuplex As Integer 
    dmYResolution As Integer 
    dmTTOption As Integer 
    dmCollate As Integer 
    dmFormName As String * CCFORMNAME
    dmUnusedPadding As Integer 
    dmBitsPerPel As Integer 
    dmPelsWidth As Long 
    dmPelsHeight As Long 
    dmDisplayFlags As Long 
    dmDisplayFrequency As Long 
End Type 
 
Private Declare Function ChangeDisplaySettings Lib "user32" Alias _
"ChangeDisplaySettingsA" _
(lpDevMode As Any, ByVal dwFlags As Long) As Long 
 
Private Declare Function EnumDisplaySettings Lib "user32" Alias _
"EnumDisplaySettingsA" _
(ByVal lpszDeviceName As Long, ByVal iModeNum As Long, lpDevMode As Any) As Boolean 

Sub ChangeMyDisplay(ByVal Breite As Long, ByVal Hoehe As Long)
 
  Dim DisplayModus As DevMode
  Dim RetVal As Long 
 
    EnumDisplaySettings 0&, 0&, DisplayModus
 
    With DisplayModus
      .dmFields = DM_PIXELSWIDTH Or DM_PIXELSHEIGHT
      .dmPelsWidth = Breite
      .dmPelsHeight = Hoehe
    End With 
 
    RetVal = ChangeDisplaySettings(DisplayModus, CDS_TEST)
 
End Sub 

Private Sub Button1_Click(Index As Integer)
 
    Select Case Index
        Case 0
        ChangeMyDisplay 640, 480
        Case 1
        ChangeMyDisplay 800, 600
        Case 2
        ChangeMyDisplay 1024, 768
    End Select
 
End Sub