I'm the new computer consultant at a small office.  They're running
off a Win2000 server.  Unfortunately, I can't add new users onto the
network, because the administrator ID and password were never
communicated to the staff.
 We can't seem to get a hold of the previous consultant(s), so we're
left in the dark.
 Is there a software tool that will allow us to retrieve this information?

Hello, pcventures:
  What you need is to reset the administrator password, this is a very
common problem on systems administration and there is a tool that has
saved me a lot of times in the past:

Offline NT Password & Registry Editor, Bootdisk / CD
http://home.eunet.no/~pnordahl/ntpasswd/bootdisk.html

Please, read the entire page because it contains a lot of useful
information you must know before do this, but basically you have to:

-Download this file

http://home.eunet.no/~pnordahl/ntpasswd/cd040116.zip

-It contains a bootable iso image you must burn to a blank cd
-Configure the computer running the Windows 2000 server to boot from
the cd drive, this is done in the BIOS
-Power on the machine and be sure the cd you burned is on the drive
-It will boot from there
-Just follow the on screen instructions

What you will do is to "blank" the administrator password, and once
this is done, you will be able to login as administrator and set a new
one.

I know all this process can be tricky, so please, don't hesitate to
request for any clarification, I'm here to help you.

Regards.

awesome answer - thanks!

www.openwall.com/john/ 
www.pwcrack.com