Onlyblue, why are you trying to use Zen Cart as a keyword? Making templates or hosting?

Zen Cart is the proper name, but keep in mind that many people will type zencart in a search field.

I would suggest going to google adwords and trying all the various combinations to see which name gets the most searches.

For instance, birdhouse is the proper spelling, but most people search for bird house so I made sure I have that keyword, and the word bird house somewhere on the site so it get's picked up.