I have a script that generates SQL for recreating logins, user, roles, and permissions on SQL 2000 databases. It may run on your 6.5 database.
It will not, however, restore passwords, and I'm not sure you can do this.
Have you thought about running the upgrade on your 6.5 databases (or a copy of them)? It's been a while, but I think this retains the old passwords.
Sorry, but I don't have a script for that. Are you sure that the upgrade process won't do this?
As a matter of fact, I think Microsoft changed its encryption algorythm between versions 6.5 and 2000, so even if you copied the encrypted value to the new server it might not recognize your password. If you are looking for a method of decrypting the password, I don't have one but I know it has been cracked (the algorythm was not very strong). You can probably find code for decrypting it on the web.