I agree with Susan, having a secure script that work properly takes time. If you're going to use the script on a busy site. Get one that already is built and tested.
Any of those scripts above are nice.
I don't run a cj site, but I do use a script for a top trade list. Which also allows you to use for a cj if you wish.
Best way to find out more is to read about it on their site. Best of all the script is not expensive at all, there is a free version and a pro verson.
Smart CGI's Intellilink
Check it out. It's pretty sweet. Oh, and if anyone gets it. Make sure you pay the little extra for the unlimited upgrades. It's worth it.