Private Const SPI_SETDESKWALLPAPER = 20
Private Const SPIF_UPDATEINIFILE = &H1
Private Const SPIF_SENDWININICHANGE = &H2
Private Declare Function SystemParametersInfo Lib "user32" Alias _
"SystemParametersInfoA" (ByVal uAction As Long, ByVal uParam As Long, _
ByVal lpvParam As Any, ByVal fuWinIni As Long) As Long 

Private Sub Command1_Click()
Dim rSuccess As Long 
 
    On Error Resume Next 
 
    With CommonDialog1
        .DialogTitle = "Hintergrundbild auswechseln"
        .Filter = "Bitmap-Dateien (*.bmp)|*.bmp"
        .FileName = ""
        .FilterIndex = 1
        .CancelError = True 
        .ShowOpen
        If Err = 0 Then 
            rSuccess = SystemParametersInfo(SPI_SETDESKWALLPAPER, 0&, .FileName, _
                                            SPIF_UPDATEINIFILE Or SPIF_SENDWININICHANGE)
            If rSuccess = 1 Then 
                MsgBox "Hintergrundbild ausgewechselt.", vbOKOnly, Command1.Caption
            End If 
        End If 
    End With 
End Sub