I used to have CS2 and used it extensively... then got a new computer with Vista.  I upgraded to CS4, and was not amused.  I am still struggling with understanding parts of it, and it seems to have a mind of its own.  I wish to go back to CS2, but that is not as compatible with my OS. It would almost be worth it to install XP on my new computer, sometimes.  Well, I'm not ready for that, yet, and I think a good book on CS4 is in my near future.  My advice is stick with the CS2, for it has a lot better tools, some of which are missing from the CS4.