I keep seeing articles that worry about not being able to do this, and I just wanted to show that you pretty much could if you wanted to (no need to buy a C64 as the Salon article author did).

I think if someone asked me how to get started hacking around, I'd suggest HTML/Javascript or Processing. They both have the advantage of being very easy to deploy the output if you want (for sharing). They also have progressive enhancement (meaning you can start knowing only a few simple things and learn more as you need it)