I use and like CS3- stick w/CS3 for now, dont needa bother gettin CS4. I hear it's not that great. CS2 is good too, just that CS3 is a lil bit more organized and nicer screen maneuverbility- but that also means you need lil bit of former knowledge of photoshop because I notice some things, like buttons- there are less than before meaning few are "hidden". As for the accountability of my advice, I've used Photoshop since 5.5

(Between the series, the CS introduce a bit of a jump but there is also a visually noticeable jump between CS2 and CS3)
I hope that helps! I'm here if you need anything.