There are lots of places that offer shopping carts to thier users. However if you decide to go with one that doesnt then you can always go to http://www.oscommerce.com and download OsCommerce for free.
Its a open source shopping cart system written in php and mysql. Your host however must support both php and mysql to use it.
Even if you do decide to go with a provider that offers a shopping cart, you might still want to look into osCommerce. It's the best free shopping cart system I've seen, truly commercial quality.
And no, I'm not involved with the project in any way.
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Are you trying to install it or just play with a demo of it. It really is a nice shopping cart, but can be a bit confusing for a newbie to it.
Another good cart, if PERL is more your speed, is City Shop from http://www.nightmedia.net