After a few hiccups I finally got Zen Cart installed and running. I don't have much experience with Zen Cart, so a few notes to remind me in case I need to revisit at any stage.
Out of the box Zen Cart is almost usable. But it requires some tweaking to make it work.
First you need a template to change the look and color away from the awful default 'Angry Hulk Green' it comes with. I cannot see any one using it, unless their mission is to drive their customers away. There are lots of free templates available for download. Google them.
After downloading your new template, its probably zipped so upzip or unRAR it. There's probably a ReadMe file inside. Read it. It contains instructions about the install of your template.
Templates are normally uploaded to /includes/templates.
Log In into your Zen Cart site as admin. Normally located at:
Go to Tools > Template Selection > Edit > Template Name > Your New Template.
After that you need to mess around with a few more things to personalize your site and add product and content.