Public Declare Function SystemParametersInfo Lib "user32" _
  Alias "SystemParametersInfoA" ( _
  ByVal uAction As Long, _
  ByVal uParam As Long, _
  lpvParam As Any, _
  ByVal fuWinIni As Long) As Long

Public Const SPI_SETDESKWALLPAPER =  20 
Public Const SPIF_UPDATEINIFILE = &H1
Public Const SPIF_SENDWININICHANGE = &H2

Public Sub ChangeWallpaper()
    Dim lngRet As Long
    Dim strFileName As String
    
    strFileName = "E:\Test.bmp"

    lngRet = SystemParametersInfo( _
      SPI_SETDESKWALLPAPER,  0 &, _
      ByVal strFileName, _
      SPIF_SENDWININICHANGE Or SPIF_UPDATEINIFILE)
End Sub