（仅供参考）

向系统菜单中添加新项，并且执行对应事件，在窗体任意位置弹出系统菜单，并且执行事件
'窗体
Option Explicit

Private Sub Form_Load()
    On Error Resume Next
   
    lhSysMenu = GetSystemMenu(hwnd, 0&)
    lRet = AppendMenu(lhSysMenu, MF_SEPARATOR, 0&, vbNullString)
    lRet = AppendMenu(lhSysMenu, MF_STRING, IDM_ABOUT, "About...")
    Show
   
    ProcOld = SetWindowLong(hwnd, GWL_WNDPROC, AddressOf WindowProc)
End Sub

Private Sub Form_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)
    Dim r As RECT
    Dim p As POINTAPI
    If Button = vbRightButton Then
        GetCursorPos p
        TrackPopupMenu lhSysMenu, 0, p.X, p.Y, 0, Me.hwnd, r
    End If
End Sub

Private Sub Form_Unload(Cancel As Integer)
    SetWindowLong hwnd, GWL_WNDPROC, ProcOld
End Sub

'-------------------------------------------------------------
'模块
Option Explicit
Public Declare Function TrackPopupMenu Lib "user32" (ByVal hMenu As Long, ByVal wFlags As Long, ByVal X As Long, ByVal Y As Long, ByVal nReserved As Long, ByVal hwnd As Long, lprc As RECT) As Long
Public Declare Function GetCursorPos Lib "user32" (lpPoint As POINTAPI) As Long
Public Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Public Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long, ByVal hwnd As Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Public Declare Function AppendMenu Lib "user32" Alias "AppendMenuA" (ByVal hMenu As Long, ByVal wFlags As Long, ByVal wIDNewItem As Long, ByVal lpNewItem As String) As Long
Public Declare Function GetSystemMenu Lib "user32" (ByVal hwnd As Long, ByVal bRevert As Long) As Long
Public Type RECT
        Left As Long
        Top As Long
        Right As Long
        Bottom As Long
End Type
Public Type POINTAPI
        X As Long
        Y As Long
End Type
Public ProcOld As Long
Public Const TPM_LEFTALIGN = &H0&
Public Const WM_SYSCOMMAND = &H112
Public Const MF_SEPARATOR = &H800&
Public Const MF_STRING = &H0&
Public Const GWL_WNDPROC = (-4)
Public Const IDM_ABOUT As Long = 1010
Public Const WM_COMMAND = &H111
Public lhSysMenu As Long, lRet As Long

Public Function WindowProc(ByVal hwnd As Long, ByVal iMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
    Select Case iMsg
    Case WM_SYSCOMMAND
        If wParam = IDM_ABOUT Then
            MsgBox "VB Web Append to System Menu Example", vbInformation, "About"
            Exit Function
        End If
    Case WM_COMMAND
        If wParam = IDM_ABOUT Then
            MsgBox "VB Web Append to System Menu Example", vbInformation, "About"
            Exit Function
        Else
            CallWindowProc ProcOld, hwnd, WM_SYSCOMMAND, wParam, lParam
            WindowProc = 0
            Exit Function
        End If
    End Select
    WindowProc = CallWindowProc(ProcOld, hwnd, iMsg, wParam, lParam)
End Function