It would be more complicated to deal with the problem when lost Windows Vista password.

Many people use passwords to protect access to computers. It is a
simple yet effective way to protect sensitive data and equipment.
Unfortunately, by their very nature, passwords can be easy to be lost
or forgotten. This can be an especially difficult problem when the
forgotten password is for Windows Vista. This is because a lot of
different functions available on XP are not available on Vista.

An administrator password cannot be changed without knowing the original password on Vista.

In Windows XP, one can change an administrator password even without
knowing its original password. Do you know how? It’s pretty easy. The
first step is to right click “My Computer”. Then in its options, choose
“Manage” → “Local Users and Groups” → “Users”. Click the targeted
account and “Set Password” for it without tying its original password.
However, if you forgot or lost an administrator password on Vista, you
cannot solve the problem in this way unless you can remember the
original password. Then, any other chances to recover the lost Vista
password?

Best way to crack Vista password—to use a password recovery software program.

If you do not mind losing data on your Vista machine, then
reinstalling your machine could be a solution. But I don’t recommend
people using this way to rescue a locked computer sine lots of time and
data will be lost. Then, to use a password recovery software program,
in my opinion sometimes could be the best or even the only way to
recover Vista password. What is the password recovery software program?
Here I would suggest Windows Password Recovery Tool Standard.

How to use Windows Password Recovery Tool Standard to reset lost Vista password?

Step1: Download and install Windows Password Recovery Tool Standard on a working PC.

Step2: Burn CD/DVD with the program.

Step3: Set the target computer boot from CD/DVD.

Step4: Reset the forgotten Vista password with the burned CD/DVD. Then log on to your Vista pc without a password.

Above are the easy steps on how Windows Password Recovery Tool
works. If you don’t have an extra CD or DVD, you can also use a USB
flash drive to replace it but at this time you need to use another
version of this tool—Windows Password Recovery Tool Professional. This
version has more functions than the Standard one, if you are in need of
Windows Vista password reset for your lost Vista admin password, and interested in this tool, you can get more information by Google search “Windows Password Recovery Tool 3.0”.

Source: http://www.blog.windowspasswordsrecovery.com/lost-vista-password.htm