Re: Zen used as plugin for CMS?
Zen Cart is not meant to be a plugin for anything. The Xoops "integration" is very old code and hasn't ever worked properly, if I remember correctly.
Your best best is to use Zen Cart as your shop and just design your template for a seamless transition from one to the other. It is much easier to keep up with upgrading both programs separately.
Please do not PM for support issues: a private solution doesn't benefit the community.
Be careful with unsolicited advice via email or PM - Make sure the person you are talking to is a reliable source.