Now, several decades later, the resources are available for the common person to create their own game. Modern video games require teams of programmers who remain virtually nameless, yet the people who choose to program for these early retro systems (Coleco, Atari, NES) can control ALL aspects of their game including plot, characters, graphics and all of the other things that go into a game. You can create an entire game by yourself. This instructable won't show you everything you need to know, but rather give you a set of resources you can use to make your own game.
A word of warning: I spent two years of my life trying to teach myself to program well enough in Assembly to make this work. Yes, the majority of games are programmed in Assembly, however there is the possibility of also programming in Basic (if you are interested, google search for batariBasic). I had no real programming experience, and while I could hack code and pretty well understand other people's code, I never was able to write my own code from scratch. You need to evaluate whether you're serious enough to see this through before you begin.
Step 1: Really, Really Assess if you are Capable of Pulling This Off
The most common mistake for newbie Atari programmers is announcing exactly what their game will be, when it will be released, and then not understanding why the retro-gaming community mocks them. It's really a miscommunication on both ends. The community has heard it before, they've seen games announced, some even have demos, and yet they never see the light of day and the author disappears. They've become a little jaded to new game announcements from new programmers, and rightly so. Most new programmers are ignorant of this and are so excited and motivated by their new-found hobby that they become a little over-zealous in their announcements. They are then frustrated and annoyed by the response they get.
I'm not trying to scare you off. I just feel it's important that you understand what you're up against before you begin. If you think you're up to the task (or just interested in the process) then please read on. I ran across this page, which does an excellent job of breaking down the tasks you face: http://www.kuro5hin.org/story/2001/9/15/211737/858