I took a look at the new Zen Cart in Fantastico. It is pretty cool. It's based on OsCommerce so it is pretty familiar to me. Has a lot of the mods (contributions) already installed and installs the PayPal IPN with the click of a button. Has a lot of other goodies in it including admin protection. Might be able to use some of my Oscommece mods on it. I'm playing with it. Worth looking at. There's an  install FAQ at http://helpdesk.lunarpages.com/faq.php?do=article&articleid=338 now for enquiring minds.  

I played with the Paypal IPN install and was able to use the Paypal Sandbox to quickly try several transactions from my store. One thing I noted, if I Continued after paying at Paypal and was sent back to my store, my store cart was emptied. If I don't Continue (as many customers don't!) but rather close the window, the transaction still went through fine at the store but my cart did not empty. I had to manually empty it. Not a big deal but something to note.