SSO for oscommerce 2.3.1 and Jcow 5

I have an oscommerce 2.3.1 site.  I also have a Jcow 5 site on the same domain in a subfolder.

I need to find a single sign on solution that will register new accounts in both, sign them in, and also sign them out of both sites.

I've created a single database and put everything in that one database.

I also made a new customers table with all fields from both of the previous customers tables, so they're basically merged into one table.  I'm not sure if it's better to use one table, or have an SSO that works in two tables.

Any guidance on this would be wonderful, as I've been agonizing over this for months, and no one has stepped up to the plate to do it for me.  My site runs on php5.

Thanks...