Commenting only Allowed for Registered Users?

Hi there, I’m setting up an e-zine for my high school at https://lantern.cioffe.com. The way it works is that I’ve hacked WordPress to only allow level 1 users to post to a single category; that category is not displayed on the main page when people visit the site. In order for a post to be displayed on the main page, an administrator (who can post to all categories) has to move the level 1 user’s post from the “Pending Approval” category to either “Poetry” or “Stories”.
What the editor of the e-zine wants however (and I hate him for this lol) is for only registered users to be able to comment on other people’s posts. Has anyone attempted this before? I have an idea of how I want to set it up, but I figured I’d asked in case anyone else had done it before and had a good idea or easier way of doing it.
Thanks guys.
Tom Cioffe
cioffe.com