Private Sub Form_Load()
    Const WM_USER = &H400
    Const TB_SETSTYLE = WM_USER +  56 
    Const TB_GETSTYLE = WM_USER +  57 
    Const TBSTYLE_FLAT = &H800
    Const TBSTYLE_TRANSPARENT = &H8000&
    Dim lStyle As Long
    lStyle = SendMessage(Toolbar1.hWnd, TB_GETSTYLE,  0 &, ByVal  0 &)
    lStyle = lStyle Or TBSTYLE_FLAT 'Or TBSTYLE_TRANSPARENT
    Call SendMessage(Toolbar1.hWnd, TB_SETSTYLE,  0 , ByVal lStyle)
End Sub

Private Declare Function GetWindow Lib "user32" (ByVal hwnd As Long, _
    ByVal wCmd 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 GW_CHILD =  5 
Private Const GWL_STYLE = (- 16 )
Private Const TB_STYLE_FLAT = &H848

Private Sub Form_Load()
    Dim hToolbar As Long
    hToolbar = GetWindow(tbarMyToolbar.hwnd, GW_CHILD)
    SetWindowLong hToolbar, GWL_STYLE, GetWindowLong(hToolbar, _
        GWL_STYLE) Or TB_STYLE_FLAT
End Sub