<p>What are the best ways of developing a subscription type website that provides lesson content (like Lynda.com)?</p>

<p>How do you protect the content from download (audio and video)?</p>

<p>What's the best way to handle passwords?
Can the user have a login name and password, and then also have an additional password that changes on a regular basis and is distributed by the site to reduce people using other people's passwords?</p>

<p>How do you minimize people sharing their passwords with other people?</p>

Protecting content is pretty easy: simply write a page which has access to the user's session / security details and check to see if they are authorized to download the file that was requested.  You could do this easily with a Java Servlet or any other web platform like ASP.NET, PHP, etc.
I would recommend against this technique of multiple passwords.  It's going to be a hassle for your customers.  It also creates the perception that you assume your customers are trying to cheat the system.  What I would do instead is log all users logins as well as user accesses for a particular file and also log the IP addresses.  You can write some code to analyze this data and look for concurrent logins from different IPs.  You could also write code to prevent multiple logins as well.