Determine the startup option by default a dual-boot Windows 7 - XP

After installation of Windows 7, dual-boot with Windows XP is Windows 7 which is positioned in the boot option by default (being the last set).On the start screen, so it is Windows 7 which is highlighted and will start automatically after the counting of the period specified.To start on XP, it will select it with the directional arrow "top" of the keyboard.To change the startup option by default,