If you've changed your user options in Win2k, we all know you could accidentally lock your self out of even administrative functions by doing something as simple as a "typo."
As long as you've built in even one power user for any purpose, you will have a chance to save many important files such as My Documents, bookmarks and more. Basically any shared files or program you have in the computer before you reinstall Windows 2000 (only option available if you've somehow locked yourself out!).
While all systems are working, create a power user to be used for emergency operations only. Set up sharing of any programs or files that you may need to save if you find yourself locked out.
When/if the lockout occurs, sign in as that power user and go to Explorer. You will find you'll have no problem accessing and backing up files set to share with this power user, but you still have a problem in getting to certain other admin only files.
The tip, or trick is this:
Go to the folder, or even program that you are now trying to backup. Map a Network Drive to it, using and Drive letter not already taken by something else. At this point, you will now be able to take over ownership of the files or program that you have mapped the Network Drive to. From there, you will now be able to take over all rights, including read, write, change, etc.
At this point, immediately copy the file or program to a backup disk, whether is be CD/RW, Floppy, or even a Zip Disk.
Systematically do this with each file or program that you are in need of copying prior to reinstalling your OS, and you will then find that after the reinstall you haven't completely lost every piece of data that you may not have backed up prior to locking yourself out.
You will not be able to save any file that was not set up for sharing, such as email, address books, etc., but you will be able to at least save such things as My Documents, and other "private" files that you really never want to lose, and are classically lost on a reinstall.
You will also find that each time you logon as that power user, Windows will have forgotten the rights that you previously assigned, so you will have to go through the Map Network Drive process for each file or program that you may missed the first time around.
After you have reinstalled the OS, you will find all users are still named in your computer, but the only user whose files are not disabled or damaged in the process are those of that particular power user. You will also then be able to retrieve the files that you had saved from the power user from the backup disks you created.
WARNING: This is a security vulnerability in the OS, and I would NOT recommend using it on a large network, but only as a safety measure on a small private network where you would normally allow all users access to these files, anyway.