If I acquire a USB QR/barcode scanner, can I set it to automatically launch a browser upon reading a URL?

Don't buy that particular scanner-- it doesn't support 2D barcodes.

Does the computer you plan to use for this have a webcam? Because that might be a totally acceptable scanner for this purpose. Then you could use software such as http://blog.odoa.eu/post/QR-Code-Scanner-for-Desktop-and-Laptop.aspx to do what you want. (I tested this. It's clearly a weekend project, but contrary to what the blog post says, it does work for me in Windows 7).

Here's another one, which I haven't tested, which looks like it might do exactly what you want (using a webcam): http://www.funcode-tech.com/Download_en.html

One concern I have is how to bring the QR application back to the foreground after viewing the web page if you don't have a keyboard or mouse. If it was me, I'd probably tinker with AutoHotKey as a way of doing this, but there are probably other ways to go.

If a webcam isn't an option, then you need to buy a 2D scanner (usually more expensive than a webcam!) And the issue of how to get to the web page becomes a little bit more complicated. That said, I think it might be possible to build the whole thing in AutoHotKey if you're using a 2D scanner.

You will need someone (or yourself) to develop a software for this purpose.

Basically you will need to capture the barcode input, use ShellExecute API to launch the web browser, and use the SendMessage API to send the text into the browser form field.

For help on programming you may try stackoverflow.com :)