There are a few resources describing how to carry out DNS recursion attacks. Is there any good explanation to help me understand how these attacks work and if systems on my network are still vulnerable?
The basic "Mother of all Recursion Attacks" was published by Dan Kaminsky.
The basic summary is that you ask for a site and provide an answer with the appropriate query idea for the recursive server before that server gets the real answer.
The best resource I've got for you is An Illustrated Guide to the Kaminsky DNS Vulnerability which describes how the recursive system worked and why the flaw was possible.