make sure the same versions of ssh are on both machines (open version 3.1+ works best for HP-UX boxes)
need to configure client (machine connecting from) and server (machine connecting to)
on client: create dsa and rsa public and private keys with the following:

cd ~/.ssh
ssh-keygen -t rsa -f ~/.ssh/id_rsa
ssh-keygen -t dsa -f ~/.ssh/id_dsa

this creates id_dsa, id_dsa.pub, id_rsa, id_rsa.pub - optionally can enter a 'passphrase' when prompted

on server:

cd ~/.ssh/

vi authorized_keys2
copy the id_dsa.pub and id_rsa.pub from client into authorized_keys file
make sure permissions 644 on authorized_keys
Also:

chmod 0700 /home/<user's-home-directory>/.ssh -R

Repeat process for creating keys on server, and copy the .pub keys to the client's ~/.ssh/authorized_keys file.

Should now be able to connect without being prompted for password.

To restart sshd: kill running sshd process
now issue:

/sbin/init.d/sshd

Or for Red Hat systems:

service sshd restart