Tente isso:
Public Const Swp_NoMove = &H2
Public Const Swp_NoSize = &H1
Public Const Hwnd_NoTopMost = -2
Public Const Hwnd_TopMost = -1
Public Const Flags = Swp_NoMove Or Swp_NoSize
Public Declare Function SetWindowPos Lib "user32" (ByVal hWnd As Long, ByVal hWndInsertAfter As Long, ByVal X As Long, ByVal Y As Long, ByVal cx As Long, ByVal cy As Long, ByVal wFlags As Long) As Long
SetWindowPos(Frm.hWnd, Hwnd_TopMost, 0&, 0&, 0&, 0&, Flags)