Answer

Vista: P1 key is defined as Initial Vista HotStart in Vista OS. You could find this utility in driver CD. After installing it and pressing P1 key when NB power off, NB will power on and execute Microsoft Media Player. If NB is power on, pressing P1 key will execute Microsoft Media Player.

XP: P1 key is defined as search function in XP OS. You could find software called System Control Manager (SCM) and reflash BIOS for XP. After installing it and reflash BIOS then to pressing P1 key, it will execute search function that bundled in OS.

Reference