In the example project, all window captions are printed to the debug window, although you could quite easily watch for any window being activated and then monitored in the background using this method.

'
' In a form, with a Timer control (timer1)
'
private Declare Function GetForegroundWindow Lib "user32" () _
        as Long
private Declare Function GetWindowText Lib "user32" _
    Alias "GetWindowTextA" (byval hwnd as Long, _
       byval lpString as string, byval cch as Long) as Long
'
private Sub Form_Load()
    Timer1.Interval = 100
End Sub
'
private Sub Timer1_Timer()
    static lHwnd as Long
    Dim lCurHwnd as Long
    Dim sText as string * 255
'
    lCurHwnd = GetForegroundWindow
    If lCurHwnd = lHwnd then Exit Sub
    lHwnd = lCurHwnd
    If lHwnd <> hwnd then
        Caption = "ActiveWidow: " & Left$(sText, _
            GetWindowText(lHwnd, byval sText, 255))
    else
        Caption = "ActiveWindow: Form1"
    End If
End Sub
'
'