You could take a backup on the 2000 server and restore it on your 2005 server. Create the same users on the new server that where on the old server. After restore run sp_change_users_login 'report' in Management studio or Query Analyzer. If names come up in the list you need to map the users in the database to the users in the 2005 server. Create a script that runs sp_change_users_login 'update_one', 'user1' , 'user1'.
See Books Online (local helpfile) for details