It just so happens that I am trying to implement a shopping cart also. So far I have setup two test systems with RedHat Interchange. It is VERY good software. Once setup, it's pretty idiot proof to administer... like a Yahoo! Store (I used to admin one). So far I've installed Interchange on Mandrake 8.1 and RedHat 7.1 successfully.

Alternatively, I was also looking at EZWebStore. This one seems easier to setup and looks attractive.