rebooting to Vista with Macbook lid closed

Hi, my wife's Macbook usually runs with the lid closed, attached to an external monitor and Windows keyboard/mouse on her desk. We haven't yet figured out a way to boot into Windows without opening up the lid of the Macbook. On a Windows-style keyboard, there is no "option" key to depress in order to bring up the OS selection screen. Is there a trick to make this happen? Thanks.