At first, i would agree this can happen easily with windows xp with the old DOS thing, but for Vista, hmmm i tried all i could but had to involve resetting the original password until I came across this simple software by
Kryptos Logic called
KON BOOT. Kon boot is a software which bypass Windows logon authentication, without overwriting your existing password, fantastic isnt it? well this software can help you enter your bosses pc without changing the existing one and after a restart, everything turns to normal like it was.
This software has Easy to use and great for information recovery, tech repairs, policy enforcement, and security auditing not only invading peoples privacy :)
the software is in a pack(zip) which was made available for cd (iso), usb, and even a floppy disk. visit the owners site
here or
here for more details and download.