So, I know I warned you in the introduction, but it needs to be said again. If you don't have any programming knowledge, Assembly is not the language to start with. If you have programming experience, Assembly is not an easy program to work in. If you learn Assembly, the Atari is particularly difficult to program for.
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