Hi Lou,
Well, you'll pretty much end up needing some sort of server-side technology for this. Odds are good you'll end up with something based on php / mysql if you want to go the open-source / cost-effective route.
Which to go with would depend largely on your situation. Google can be your friend here. Something like "open-source shopping cart" can be a big boon.
Your major players are probably going to be ZenCart, osCommerce, and Magento. ZenCart and osCommerce are older solutions and a bit easier to deal with. Magento is kind of a beast to get started with and to set up, but is the most fully-featured open-source solution available. Not for the faint of heart though.
If you have any thoughts of building a site on a Content Management System (which has a lot of benefits in and of itself) I would recommend going with Joomla!. That opens up the possibility of using VirtueMart or any of the various extensions that let you set up a wide array of shopping carts.
This may be the best option for someone with little php / mysql knowledge as most of the heavy lifting has already been done for you, but there's a bit of a learning curve when it comes to learning how to use Joomla.
There also may be some services that you could go with where you list your products on some sort of hosted environment. Many of those take a cut of your sales though. I'm sure with a bit of time on Google you could find something like this.
I think that pretty much enumerates the options. eCommerce always makes things a bit trickier, since you have to deal with security and a lot more testing to make sure everything is set up correctly and bug-free.
