Thanks everyone who has suggested ideas.
Interspire have just informed me they are currently creating a new shopping cart product which will easily integrate with ArticleLive. I have been very impressed with ArticleLive so I am going to see what this new product is like before changing. The new product is out in the next 3 months.
I recommend using an open source shopping cart such as osCommerce. I`ve gone the paid route (monsterCommerce), as well as the free route, and I have discovered many more technical problems with the non open source ones.