Hi, until now I have created a number of sites that are online catalogs for small businesses, all of them run off of a access database with complex structures to hold the product info...none of these sites have required shopping carts up until now...so I have not created anything to deal with orders, customer login, credit card processing order tracking and so on... does it pay to create all this or is there a good system that I can use (third party) that can work with what I already have...for example for one site they did want to use paypal - which was simple to use with my existing structure - is there something like that a bit more sophisticated that I can use with what I have...any suggestions would be appreciated...

Depends on what your client wants. I've created simple shopping cart/checkout page that routs to ViaClicks payment processing in a matter of few hours, and I've worked on some enterprize solutions that took 6 months to complete. Let the scope be your guide :)