There's a utility to rebuild the master database. You will lose all logins, all server-level roles and permissions, all linked servers, you'll have to reattach all user databases.
Google for rebuild master SQL 2000.
Why no backup?
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability