"How do I change what the start menu power button does in Windows Vista?"
Click on the Start/Windows icon in the lower left hand corner of your screen and type "power options" in the <i>start search</i> text field. This will take you to Control Panel\Power Options.
More information on the power settings is
available here on the Microsoft Answers site, as well as on the Windows Vista Help pages>Windows Vista Help pages</a>. There are also several third-party tutorials are available on the Internet.
Hope this helps.