actually you can do it with an outside program. I've used one from wasp barcode. it can be configured to do a sequence of events after each scan. it's great for shipping etc. Scan the order number and tracking number, and the web system, sends them a confirmation email, checks the order as shipped etc...
The issue here is I already have a fully functioning web-store which is doing the job brilliantly - the barcode implementation is for rapid entry of product details to add to stock or an order etc... That's why I want to do this with a purely web-based approach (or am I missing something?)
i did this about 2 years ago, so memory is a bit vague
also helps to have your own special barcode for "submit" etc - stick that to the side of the PC so you can scan it any time you need to - i had a couple of other special codes of my own to do other things like this
just check that the scanner you want to use will read the barcodes on your products