No, you can't integrate XPO on a Joomla website, however, Joomla is a very flexible CMS which gives you the power to transfer your CMS site into an auto shop in easy steps with the help of scripts and modules. There is one called Shopping Cart. It can be accessed through Google. Additionally, there is the possibility to use an opensource script created exactly for these type of businesses. It's called OsCommerce and it can be installed on your host.