Conversion from another cart without losing our site's current look and rankings

we have a website built with PHP3 and a new account with a web host employing PHP5. It is our hope that we can employ Zen Cart on our site with minimal change to the site's appearance and functionality and importantly continue to retain it's ranking with the search engines. We have HTML experience but no PHP. Is it possible to make this change with some ease or are we walking into a lion's den?

You can't just plug Zen Cart into the backend of your current site. You will need to recreate your site's look and feel in the Zen Cart template system. You can probably import much of the database info after proper massaging to get it into a ZC-compatible format.
You will need to 301 redirect your current URLs to the Zen Cart generated ones, or you could use the free CEON URI Mapping addon with its (commercial, but reportedly worthwhile) URI Mapping Manager to keep your current URLs.

Don Richardson:

We have HTML experience but no PHP. Is it possible to make this change with some ease or are we walking into a lion's den?

It will be a lion's den, I'm afraid.

As Glenn says, zencart is not designed to be a "plugin" shopping cart - it is a sophisticated CMS in its own right, with the core focus on eCommerce.

A highly skilled php/mysql developer will probably be able (with a team of helpers) to "mash" the two together, but it is not recommended.

Unless there are some very special bespoke functions to your current site that cannot be replicated in zencart (or perhaps modularised for zencart) then you should just abandon your current structure and go for native ZC.

There are options:

Install zencart as a fully functional "shop" - either as a sub-domain, or in a separate folder in your current site. This gives you:

http://shop.yourwebsite.com
or
http://yourwebsite.com/shop

Create a new domain entirely, and point visitors to this domain if they want to do shopping.

Oh... and while knowledge of HTML is useful, it is a very different animal from php...

The learning curve can be a bit steep.

gjh42:

You will need to 301 redirect your current URLs to the Zen Cart generated ones, or you could use the free CEON URI Mapping addon with its (commercial, but reportedly worthwhile) URI Mapping Manager to keep your current URLs.I agree TOTALLY with this.. the URI Mapping Manager is a worthwhile purchase..