Scott posted yesterday on a new series about SSH coming to Apple Matters. If you want to skip the learning and go straight to the Secure Shell-ing, then why not take a look at this recent post by John Welch. In this post, he describes how to set up a simple AppleScript that uses Apple Remote Desktop to SSH into a set of Macs on your local network. The script takes the machines you have selected in ARD (or, if you've only got one selected, just that machine) then opens SSH sessions in Terminal, ready for you to type your UNIX commands to your networked computers.
If you want to get the script and start batch-connecting to your machines, visit his website.