程序代码：

Option Explicit
Private Type POINTAPI
    x As Long
    y As Long
End Type

Private Declare Function GetDesktopWindow Lib "user32" () As Long
Private Declare Function GetWindowDC Lib "user32" (ByVal hwnd As Long) As Long
Private Declare Function ReleaseDC Lib "user32" (ByVal hwnd As Long, ByVal hdc As Long) As Long
Private Declare Function Ellipse Lib "gdi32" (ByVal hdc As Long, ByVal X1 As Long, ByVal Y1 As Long, ByVal X2 As Long, ByVal Y2 As Long) As Long
Private Declare Function CreatePen Lib "gdi32" (ByVal nPenStyle As Long, ByVal nWidth As Long, ByVal crColor As Long) As Long
Private Declare Function SelectObject Lib "gdi32" (ByVal hdc As Long, ByVal hObject As Long) As Long
Private Declare Function DeleteObject Lib "gdi32" (ByVal hObject As Long) As Long
Private Const PS_SOLID = 0

Private Sub Command1_Click()
Dim x As Long
Dim y As Long
Dim deskHwnd As Long
Dim hDeskDC As Long
Dim hPen As Long

x = Screen.Width / Screen.TwipsPerPixelX / 2
y = Screen.Height / Screen.TwipsPerPixelY / 2

deskHwnd = GetDesktopWindow()
hDeskDC = GetWindowDC(deskHwnd)
If hDeskDC = 0 Then Exit Sub

hPen = CreatePen(PS_SOLID, 2, vbRed)
If hPen = 0 Then Exit Sub

SelectObject hDeskDC, hPen

Ellipse hDeskDC, x - 10, y - 10, x + 10, y + 10

DeleteObject hPen
ReleaseDC deskHwnd, hDeskDC
End Sub