QUOTE(DMW @ Mar 10 2007, 08:39 AM)

This is a good question, I wish someone would answer it. I have the same question.
Basically you either write your own db application (which is not a vast job, but takes a lot more than an afternoon), or you use a prewritten system, such as oscommerce, which you customise following their instructions. If you write your own, you need to be familiar with a programming language (e.g. PHP), and read enough of the db manual (e.g. Mysql) to be able to write the calls to access the db. Something like Mysqladmin[?] may be a good way to set up and manage the database.
The basic tables in the database are not so complicated: you need a table with one entry for each trailer / jigsaw puzzle / gizmo-whatever, with fields for the product code, the title/name, description, price, stock level, and so on. At the simplest you only need to write one function called show_prod($pcode), where $pcode is the code identifying the product, and this function generates all of the html for a single item, including PayPal links, or whatever. You can manage the stock levels manually when an order arrives. The great thing about writing your own is that you can easily add all the features that are particular to your particular system, such as being (semi)bilingual, or features specific to the product - jigsaw puzzles have a landscape/portrait/other flag, where trailers don't, for example.
Disclaimer: I wrote my own, and haven't used oscommerce, mysqladmin or any similar systems. I have no idea just where with such systems you would hit the wall, and discover that there was no way (for example) to include a database of artists (such as I need). Ultimately oscommerce etc are Solutions, whereas php/mysql is a set of Tools. You really have to learn how to use Tools, whereas all you have to do with Solutions is use them, until you discover somewhere that your problem is not the one to which the Solution is, um the solution, and you have to start solutioneering, converting your problem to the one that the Solution addresses.