As root, install the software:
apt-get install libpam-opie opie-server
Comment out the old auth line of /etc/pam.d/login and /etc/pam.d/ssh:
#auth required pam_unix.so nullok
Add the new auth lines, permitting either OPIE or standard unix password logins:
auth sufficient pam_opie.so auth sufficient pam_unix.so nullok auth required pam_deny.so
continued...