unless you are using the default templates, going the css route is probably less work than trying to manipulate the default tables.
already have two 3dcart sites that are over 90% css (not worth it to change every template file). regarding the alternate css... unfortunately microsoft's trash browser (ie6 in particular) almost requires this. most every browser will understand css and display it just fine, then you go back and fix for internet explorer, which looks something like this:
Code:
<!--[if lte IE 6]>
<LINK REL="StyleSheet" HREF="assets/templates/[template]/css/ie.css" TYPE="text/css" MEDIA="screen">
<![endif]-->
<!--[if lte IE 7]>
<LINK REL="StyleSheet" HREF="assets/templates/[template]/css/ie7.css" TYPE="text/css" MEDIA="screen">
<![endif]-->