I've installed LinkMachine on my web site, but when I run the script linkmachine.php, I am presented with a page full of nonsense text that begins with a copyright notice. What is wrong?

What you are seeing is the LinkMachine script itself. The problem appears to be that your web server does not support Php scripts. So rather than running the script, it is simply showing you the script as text. Unfortunately the only way to get LinkMachine working on your site would be to move your site to a web host that does support Php. The majority of hosts do support Php - a couple that I recommend are ThinkHost and 1&1.