The NOP cart system is absolutely the greatest java script ever! I found it to be extremely easy to configure and had it up and running on my clients website within a couple hours.
Clients Website: http://www.dawgbed.com
It is advised that anyone using this script for their business should review the topic (Managecart Security Flaw) under the modifications forum http://www.nopdesign.com/forum/viewtopic.php?t=2345.
Randy was kind enough to supply the code to patch this hole to ensure the safety of your shopping cart sales.
Best of Luck