codice:
Private Declare Function GetForegroundWindow Lib "user32" () 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 GetDC Lib "user32" (ByVal hwnd As Long) As Long
Private Sub Form_Activate()

    Dim Ret As Long
    Do
        'trova dove disegnare
        Ret = GetForegroundWindow()
        'trova l'handle
        Ret = GetDC(Ret)
        'disegna x,y,base, altezza
        Ellipse Ret, 0, 0, 200, 200
        DoEvents
    Loop
End Sub