One suggestion that will save you much time and energy is to download a free 800xl emulator and then download the game roms. As I understand it, it is legal to download a game rom so long as you own the game. You are allowed one extra copy of any game you own for archiving purposes. If anyone thinks this is incorrect, please respond.
However one site http://members.xoom.com/atari800/ has links to many emulators. The one that I like is XL it.
This way you can avoid the complex process of buying a cable to hook up your Atari disk drive to your Computer.