Public Function LoadIcon(IconFile As String, Optional iWidth As Long = 16, _
  Optional iHeight As Long = 16) As Long
 
LoadIcon = LoadImage(App.hInstance, App.Path & "\" & IconFile, IMAGE_BITMAP, _
  iWidth, iHeight, LR_LOADFROMFILE)
 
End Function

Public Sub SetIcon(Frm As Form, mMain As Long, mSub As Long, IconHandle As Long)
 
Dim MenuBar As Long
Dim Menu As Long
Dim SubMenu As Long
 
'Handle der Menüleiste
MenuBar = GetMenu(Frm.hwnd)
 
'Handle des Menüs (von links)
Menu = GetSubMenu(MenuBar, mMain)
 
'Handle des Eintrages im Menü (von links)
SubMenu = GetSubMenu(Menu, mSub)
 
'Icon setzen
SetMenuItemBitmaps Menu, mSub, MF_BITMAP, IconHandle, 0&
 
 
End Sub

IconHandle = LoadIcon("ico_new.bmp")
SetIcon mdiMain, 0, 0, IconHandle