Option Explicit
 
Private Declare Function SetLayeredWindowAttributes Lib "user32" (ByVal hWnd As _
  Long, ByVal crKey As Long, ByVal bAlpha As Byte, ByVal dwFlags As Long) As _
  Long
Private Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" ( _
ByVal hWnd As Long, ByVal nIndex As Long) As Long
Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" ( _
ByVal hWnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
 
Private Const GWL_EXSTYLE = (-20)
Private Const LWA_ALPHA = &H2
Private Const WS_EX_LAYERED = &H80000
 
Public Function MakeTransparent(ByVal hWnd As Long, Perc As Integer) As Long
On Error Resume Next
    Dim Msg As Long
 
    If Perc < 0 Or Perc > 255 Then
        MakeTransparent = 1
    Else
        Msg = GetWindowLong(hWnd, GWL_EXSTYLE)
        Msg = Msg Or WS_EX_LAYERED
        SetWindowLong hWnd, GWL_EXSTYLE, Msg
        SetLayeredWindowAttributes hWnd, 0, Perc, LWA_ALPHA
        MakeTransparent = 0
    End If
 
    If Err Then
        MakeTransparent = 2
    End If
End Function