I could detail many things between the OS's, excluding the Mac, sorry but never had the money for one, I just build my own PC's.
The main thing with Windows 7 is that it is the true next OS after XP, Vista was a fluke. Though as I said getting something like pro or higher 7 is good if you are into messing a lot with the basic structure and want access to XP mode, allowing older programs to run, due to the kernel change most don't on 7. I currently switch to 7 about 6 months ago and haven't had any major issues that I did with vista. There is admitting some older games that have issues, ones that were programmed on XP, but not always.
Ok enough random tech talk, I am bad about explaining things unless I am ask a specific question.