Start by changing the width here and in .homepage_productbox hover to 159:

.homepage_productbox{ width: 219px; overflow: hidden; float: left; background: url( ) left top no-repeat;}

and remove the min-height: property in the .homepage_productbox hover rule.

You'll probably want to fiddle with margins and padding in all of the homepage_productbox rules.

It's a mystery to me why template designers add all theese extraneous divs and ids when Zencart, with the proper mods, displays the product listing just fine.