VirtueMart (formerly known as mambo-phpShop) is the leading Online-Shop solution for Joomla and Mambo.
VirtueMart is a free shopping cart software! You can download, use and modify it without any restrictions (License: GNU/GPL) - just as Joomla. VirtueMart is no stand-alone script, but a shopping cart plug-in and requires the PHP Content Management System Joomla! (or Mambo).
So you must install Joomla first, then VirtueMart. The easiest way is to install the a ready-steady-go bundle of Joomla Ecomerce Edition, a pre-installed VirtueMart. A lot of translations are available: addtional language files can be found in the Language Pack