You want to run ssh-agent in the parent login shell, so later shells inherit the SSH_AGENT_ID and SSH_AGENT_PID environment variables. If you use bash, then .login or .bash_login should contain something like:
eval `ssh-agent` /Allan -- Allan Wind Life Integrity, LLC http://lifeintegrity.com -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org