I have some machines with RHEL4 Nahant Update 6. Oddly, I found that passwords longer than 8 digits are not stored.
So if I had a password 1ABCDEa!, and I changed it to 1ABCDEa!1ABCDEa! I could still log in to the machine with the old password.
This machines use NIS authentication, but other machines with Red Hat 5 which use the same NIS server allow login ONLY with the NEW password (16 digits long...)!