Reset forgotten local admin password on Windows

- Boot from DVD Windows boot media
- Choose "Repair your computer" command line option
- Launch "cmd"
- Go to "c:\windows\system32"
- Rename "Utilman.exe" to "Utilman.exe.bak"
- Copy "cmd.exe" to "Utilman.exe"
- Reboot

- Do the keyboard shortcut "Windows + U" when on the logon screen and an
super-admin console will appear
- Type "net user administrator Newpass123" to reset password or create a
new account
- log on

- Make sure you revert the "Utilman.exe" back to original version, you will
need to boot from DVD to get access

Source:
http://lordoftheping.blogspot.com.au/2009/05/i-did-not-use-my-tests-virtual-machines.html