what OS are you trying to bypass? Is it XP, 2000, 2003 Server? Is this system on a domain?
There are programs like In Code We Trust or the Ultimate Boot Disk that you can boot from a CD with that will allow you to reset the administrator password on these systems.
If you have accessibility options enabled and no hard disk encryption, try this…
Boot to installation media and get a cmd prompt
run the following commands:
copy c:\windows\system32\magnify.exe c:\windows\system32\magnify.exe.old
copy c:\windows\system32\cmd.exe c:\windows\system32\magnify.exe
When prompted to login, click the accessibility button (bottom left) and place a check next to screen magnifier. This should launch a command prompt window with system level privs. You can now *safely* change the administrator’s password.