Well it all depends on what you will be using it for, Cs3-Cs4 would be best because it's up to date. But the thing I like is the Photoshop toolbars and layout stayed similar throughout the years. The biggest thing is when looking for brushes most will be for Cs and up more than likely, so Cs-Cs4 would be best but if you can't get ahold of them then work with what ya got.
CS4...but it really doesn't matter which. For a while I was using Photoshop 7.
ImageReady or AnimationShop would be your best bet. I would personally prefer imageready as you could find more tutorials out there. And I just find it easier to use especially if you have Photoshop experience.
At first I saw this and thought it was any question and answer. But alas, it's just for you artistically and technologically advanced folk.
Stupid question to you, necessary to me: what is needed in order to make a gif?