If your developing a shoping cart.. I suggest you use a cookie to store the information. This is how most people do it.

Im assuming your using an IIS server so.. you can use the unique session id that is generated by IIS. So just store all the pending item info in a cookie and then upon checkout then have the customer login and then process and log the transaction. This will also take a huge load off your server because if you consider that your going to have to create a cart for everyone that visits the pages.

Eric