copying users/pwd from one box to another

hi, I'm running some servers and I would like to change one of the server with another box, that is more "up-to-date" regarding the CPU/Memory/Disk and OS... The old box is run by a RH6.0 and the new one will be a SuSE 7.0... the question is, how can I move all the users if i tell you that i don't want the passwords to be changed... The box existed long before I was here, so i don't know every password (especially our customers password). Is it possible to copy one password file from one box to another in order to keep the same passwords for all the users ?.... and is there a sure way to transfer all users once for all whithout any doubt ?... TIA Stephane Parenton