This is well known information; Google should help you find it. There are many ways to crack the password on Windows XP, Hiren’s boot CD has a tool to reset the passwords but if you want to find out what the password is us Ophcrack live CD. You can even reset the password from the command prompt. Vista and Windows 7 are a bit trickier but can still be done, so you shouldn’t trust the windows password to protect your computer.