There is a good 2D tutorial series at http://fixbyproximity.com/2d-game-development-course/" href="http://fixbyproximity.com/2d-game-development-course/">http://fixbyproximity.com/2d-game-development-course/" href="http://fixbyproximity.com/2d-game-development-course/">http://fixbyproximity.com/2d-game-development-course/
This will give you a great introduction to using Allegro 5 to build a 2D game. Technically its in C++, but this course doesn't us OO. There is a follow-up course (also on that site) which redoes the same game in a more OO methodolgy, but you need to do the other course first because its the one that actually explains Allegro
oh yeah this assumes you at least understand C/C++ already
How much C++ do you think we need to know before we can start?
You don't need to know anything to start(you can learn as you go if you really want to) but the more you know the easier things will be and the less likely you'll be to run into a brick wall. (The bigger your game is the harder it will be to avoid creating an unmanagable mess)
Keep your first game simple, If you havn't made a pong clone yet i'd strongly recommend that you make one, it will give you the basic idea of how games work and give you a better idea of where you stand).