Rick - You need to wrap each beer in bubble wrap. Then, take 2-3 beers and tape them together so they can't rattle. Make sure the box is sturdy and there is padding all around the box. It's also good to place the wrapped bottles in a small trash bag and tie the bag off to limit leakage if breakage occurs.
I've mailed plenty of booze over the years and never had any break. Of course, it's illegal (according the U.S. Post Office) to mail alcohol and they usually ask me when I mail. So, make sure you can't hear shloshing when you move the box. My post people listen for the shloshing and jack me. I usually tell them it's olive oil.
