What's the difference between the Photoshop Creative Suites?

I’m looking at Adobe Creative Suites with Photoshop, and going crazy. Photoshop Creative Suite 5. Photoshop Creative Suite 5 Extended. Creative Suite 5.5.

The first two seem to be just Photoshop, but what does “extended” add?

The third seems to have Illustrator and Acrobat and a few other pieces of software. Also it’s 5.5. What the difference between 5 and 5.5? Why does Adobe Photoshop 5 extended cost the same as Creative Suite 5.5?

Then there are teacher and student versions. And a bunch of other versions that cost even more. Some have more software. Some seem to be the same thing. Help!

My son wants Photoshop, and at first we were,like, “no way” because it costs $800, but then I discovered we can get the student pricing, which cuts the cost to a quarter the official price. We haven’t told him this. But I can’t figure out what version is best and whether it’s better to get all the software you can, or if the suite leaves out things and so we should get version 5 with only photoshop or what.