As always, the only way anybody has ever thought of to "plan" software is:

    1) write down everything you're going to do
    2) write down how long that's going to take
    3) add them all up and voila!  You have a schedule!

The ways this breaks down in practice would be comical if not for the fact that everybody takes it so seriously. The biggest problem is that step 1 takes longer than the actual software development task all the time, every time. That might not be _so_ bad other than the fact that it's also always completely wrong.