Possibly stupid question

I'm running Zen Cart (1.3.8a) on my nephew's site as CMS.

How badly will it screw up the site if we want to add an actual product to it? He'd like to be able to sell his book from the site.

Not sure how using Zen Cart for what it was designed for will screw things up?

Can you be more specific about your concerns?

Basically, I have the shopping cart part of Zen Cart turned off. All the "products" are document general since they're articles he's written. I don't know if adding a "real" product will interfere with the existing "products".

I've been considering creating a 1.3.9h version of the site as a test and adding the book to it as a product. That way I can test both 1.3.9h with an eye to upgrading AND see what effect activating the cart would have.

A test area is always a good idea.

Document General and Product General are two different animals that play nice together within Zen Cart. I don't see any problems. As always though, layout and customizing are where you will probably have the most difficulty but shouldn't be too difficult for what you want.