If you want to prevent sshd from running automatically, you can remove it from runlevel 2 by using the update-rc.d script. Alternatively, you can prevent the init.d script from starting the daemon by creating a file in ssh config directory (which you would have to (say) rename in order to start the daemon manually):
touch /etc/ssh/sshd_not_to_be_run.

Not sure if removing the init script from the runlevel would prevent it from respawning, though.