I did a search and found that SQL 2000 does have a system procedure called sp_change_users_login

which does fix the database login to match the SQL Server instance.

MSDN link is:

http://msdn2.microsoft.com/en-us/library/ms174378.aspx

Format I ended up using is: (Note, I've left off the optional SQL User (if you are mapping to a different user) and password at end):

USE your_database

GO

EXEC sp_change_users_login 'Auto_Fix', ' '

GO