Hello,
' I'm 'Shell'ing Photoshop Elements, which
' takes awhile to get settled.  Using
' Sendkeys "{END}", True and then
' WaitForInputIdle(..) does the job,
' but the Wait, although correctly waiting,
' always returns -1&=WAIT_FAILED.
' It should be 0& (or &H102&=WAIT_TIMEOUT).

' Q - why WAIT_FAILED?

' Run this routine, then open any another application.
' It prints the hWnd, Class, Title, and the
' time it takes for WaitForInputIdle.
' That can be over 1 second for Photoshop.
' This is all XL97/WIN98.  D-C Dave

' API Declarations
Declare Function GetClassName& _
 Lib "user32" _
 Alias "GetClassNameA" ( _
 ByVal hwnd As Long, _
 ByVal lpClassName As String, _
 ByVal lLen As Long)
Declare Function GetForegroundWindow& _
 Lib "user32" ()
Declare Function GetWindowText& _
 Lib "user32" _
 Alias "GetWindowTextA" ( _
 ByVal hwnd As Long, _
 ByVal lpString As String, _
 ByVal lLen As Long)
Declare Function GetWindowThreadProcessId& _
 Lib "user32" ( _
 ByVal hwnd As Long, _
 lpdwProcessId As Long)
Declare Function WaitForInputIdle& _
 Lib "user32" ( _
 ByVal hProcess As Long, _
 ByVal dwMilliseconds As Long)

Public Const WAIT_FAILED = -1&
Public Const WAIT_TIMEOUT = &H102&
Public Const INFINITE = -1&

Sub TraceForegroundWindows()
 Dim hWndNew&, hWndOld&, Pid&, Tid&, s1$, l1&, zTime1!
 Do ' forever until you stop it
   hWndNew = GetForegroundWindow()
   If hWndNew <> 0 And hWndNew <> hWndOld Then ' if new FG window,
     hWndOld = hWndNew
     
     ' print window stuff
     zTime1 = Timer ' beginning time (secs)
     Debug.Print "hWnd:  " & hWndNew & ", " & FormatSecs(zTime1)
     Debug.Print "Class: " & zGetWindowClass(hWndNew)
     Debug.Print "Title: " & zGetWindowTitle(hWndNew)
     
     ' wait for it to settle and print delay
     Pid = GetWindowThreadProcessId(hWndNew, Tid)
     SendKeys "{END}", True ' some input
     l1 = WaitForInputIdle(Pid, (INFINITE))
     ' I never get anything but WAIT_FAILED,
     ' but yet it does wait.
     If l1 <> WAIT_FAILED Then Stop
     Debug.Print "Delay: " & FormatSecs(Timer - zTime1) & vbCrLf
   End If
   DoEvents
 Loop
End Sub

Function zGetWindowClass$(phWnd&)
 Dim s1$, l1&
 s1 = Space$(260)
 l1 = GetClassName(phWnd, s1, 260)
 zGetWindowClass = Left$(s1, l1)
End Function

Function zGetWindowTitle$(phWnd&)
 Dim s1$, l1$
 s1 = Space$(260)
 l1 = GetWindowText(phWnd, s1, 260)
 zGetWindowTitle = Left$(s1, l1)
End Function

Function FormatSecs$(pT!)
 Dim HH%, MM%, SS!, sHH$, sMM$, sSS$
 HH = Int(pT) \ 3600&
 MM = Int(pT - HH * 3600&) \ 60&
 SS = pT - HH * 3600& - MM * 60&
 sHH = Format(HH, "00")
 sMM = Format(MM, "00")
 sSS = Format(SS, "00.000")
 FormatSecs = sHH & ":" & sMM & ":" & sSS
End Function