Has anyone seen - or used - a shopping cart script, probably Java, that looks and acts like Google Checkout?

I like the GCO floating window, so as a customer scrolls down my list of DVDs to buy, the Java window comes along for the ride... and as the customer adds to cart, the floating window updates items, quantities and $ amount.

2 1/2 years ago I hand wrote a PHP shopping cart, which is great, but it uses Session Arrays, and lately those cause things to slow down.

I always did like the GCO window, but I need this to then click on to CCBill checkout.

Thanks in advance,