Recently a Falls Church, Virginia customer called me to help them get into their computer after they forgot their Windows login. They were locked out of their own computer. Luckily for them (and unluckily for most people), the passwords can be found using brute force and dictionary cracking tools.
There are many programs to recover the Windows XP and Windows Vista passwords. My favorite is Ophcrack. Download the Live CD, burn the iso to disk (not as a file but as a disk image), and boot the computer off the disk.
Ophcrack will start automatically and typically take 5-30 minutes to determine all the passwords that it can. The shorter the password, the faster Ophcrack can find it. Unless there is a very long password (over 14 characters), Opencrack will be able to tell you what it is.