First off, "the one file"=???
Second, you shouldn't be inputting < and > into your php document unless you're trying to output them to the browser - do not use them for actual php control structures or code. Unless I'm profoundly misunderstanding what you're doing here, I'm pretty sure that's wrong.
Lastly, you don't need to escape the double quotes in your include line (the error that you're receiving). Your final code should look like:
$myclass = &new ClassName;
Edit: and might I suggest that you tack a .php extension onto your class file? Not all web servers know what to do with .class - so it's very possible that if someone were to go to http://yourwebsite.com/ClassName.class
they'd see your code (dangerous). If you put a .php extension on the end, the web server will not show any of your code to the user.