Google for shopping carts such as Zencart and Cubecart..those are the best shopping cart scripts imho. Customizable, pretty much just need to get a design and then configure the cart, and add products.
I think it's not that hard and maybe this is why most my clients now want shopping carts. i had a good experience with oscommerce, as weird as it may seem sometimes. Once you find out how to tame the beast it's pretty good.
I use roman cart and osCommence and both have there better fetures.
It is a kinda software on the web were you can add prodocts to there product manerger and have links to your own shopping cart. The product manager lets you make a code in html which you add to any webpage.
Romancart costs from free to $369.99 per year.
oscommence is free and it is a php and db program which allow you to add products and you have to use there website setup to make the e-commerce part of the site.
You need to do some reseach before you deside and if you need any questions answered add me on msn or yahoo.
I think two aspects are very important and need your promotion: firstly, attract visitors and turn them into customers, this is the most important and the hardest. Secondly, an easy and quick order step for customers.