[dba-SQLServer] Rolling Back Transactions

Group,

SQL2000 - We had a situation where a client ran a procedure that 
changed a large number of transactions.  When it was finished she 
realised that she made a mistake, and wanted to be able to undo the 
changes.  No backup was made of the database just prior the changes 
of the records (although we do have earlier backups and transaction logs).

Does SQL have a facility to be able to undo the changes?  I tried 
looking through Books Online but could only find restoring from 
previous backups and transaction logs.  I couldn't see anything about 
undoing transactions, or restoring parts of transaction logs.