This procedure has been tested and does work on both Windows Nt4 and Windows 2000. In order to accomplish this, do the following:

FAT-16/FAT-32 File system - THE EASIEST

You need to have a bootable DOS disk (preferably a 98 startup disk or its equivalent) or the ability to dual-boot to an operating system other than 2000/NT4 on the same drive.
You must have the ability to write to the hard drive where 2000/NT4 operating system is installed (WINNT).
Make sure your boot disk includes the ATTRIB utility.
Boot up the system with your DOS disk and come to the A: prompt. Change to the C: drive.
3.) CD to WINNT\SYSTEM32\CONFIG
4.) Run DIR to look for the file “SAM” (has no extension and is approx 20K+ in size)
5.) Be prepared to run the ATTRIB utility to check file attributes, if needed.
6.) Delete the SAM file.
7.) Reboot. Press Ctrl-Alt-Del to Logon, Press Enter to get back to the desktop.
Set a new password for Administrator.

NTFS File system - INCREASING LEVELS OF DIFFICULTY You still have the same basic choices when recovering an Administrator password under a NTFS file system:
you must either crack it or forcefully reset it to something known.
It seems that resetting the password will take much less time than brute force cracking and require far less skill.
In cases where the NTFS file system is being used, the practice of deleting the SAM file can still be accomplished as long as you have the ability to WRITE to the hard drive where the 2000/NT4 operating system is installed (again WINNT).

Here are some possible choices on how to proceed.
You could:
1) Carry out a format/reload.
2) Reinstall a second copy of 2000/NT4 (parallel install into a new folder like WINNT40), then access the other version of NT (WINNT folder) and delete the SAM file at the same location noted above.
However, this would require a number of additional decisions, such as considering the amount of available disk space, potential compatibility issues, all potential time wasters.
3) And finally, if the client doesn’t want to format (client has data or user accounts they want to keep) and can’t reload (for either some of the same reasons already stated or whatever else), you can still recommend that they go to www.winternals.com and find out about the costly utilities available there such as NT Recover, Locksmith, or NTFSDOS PROFESSIONAL.
At their own risk and without your support, the client is then presented with additional options which would allow them to either clear or change the Administrator password and in some cases retain all their user accounts.
These utilities will allow them to avoid the format/reload or the reloading of another copy of the operating system, if they are willing to pay for it.