C#

private void activateWindow(IntPtr hWnd)
{
    if (IsIconic(hWnd))
        ShowWindowAsync(hWnd, SW_RESTORE);

    ShowWindowAsync(hWnd, SW_SHOW);

    SetForegroundWindow(hWnd);

    IntPtr foregroundWindow = GetForegroundWindow();
    IntPtr Dummy = IntPtr.Zero;

    uint foregroundThreadId = GetWindowThreadProcessId(foregroundWindow, Dummy);
    uint thisThreadId = GetWindowThreadProcessId(hWnd, Dummy);

    if (AttachThreadInput(thisThreadId, foregroundThreadId, true))
    {
        BringWindowToTop(hWnd);
        SetForegroundWindow(hWnd);
        AttachThreadInput(thisThreadId, foregroundThreadId, false);
    }

    if (GetForegroundWindow() != hWnd)
    {
        IntPtr Timeout = IntPtr.Zero;
        SystemParametersInfo(SPI_GETFOREGROUNDLOCKTIMEOUT, 0, Timeout, 0);
        SystemParametersInfo(SPI_SETFOREGROUNDLOCKTIMEOUT, 0, Dummy, SPIF_SENDCHANGE);
        BringWindowToTop(hWnd);
        SetForegroundWindow(hWnd);
        SystemParametersInfo(SPI_SETFOREGROUNDLOCKTIMEOUT, 0, Timeout, SPIF_SENDCHANGE);
    }
}

IntPtr originalWHwnd = GetForegroundWindow();   //To keep the handle of the window in which the user is currently working.

/* Let's say that window with handle "hWnd" must be visible now: */
activateWindow(hWnd);  //It works in Vista and XP: brings the window to foreground.

/*
    Here I do the stuff with the window "hWnd":
     - move the mouse somewhere,
     - click somewhere else...
     */

/* Finally I want to bring back the original window: */
activateWindow(originalWHwnd);  //It does not work on Vista; it does on XP.

Microsoft.Office.Interop.Outlook.Items MyItem=mItem.Items;
MyItem.Sort("Received", false);
foreach(Microsoft.Office.Interop.Outlook.MailItem item in MyItem)
{
....
....
}