Hi Mikwd,
The main difference between the software vs. sitebuilder is that Sitebuilder offers an easy, out of the box solution for your shopping cart. Graphics and title/site name is all integrated within your site. With that being said, many downloadable shopping carts out there have similar templates(Themes) that you can customize with minimal programming skills. Os Commerce is probably the most popular one and we offer a 1 button install for you in our control panel. No need to download and install on your own
:
http://www.oscommerce.com/I would give both a try since the sitebuilder have a 60 day money back guarantee.
Hope that helps.
Tony