download trial, and test cs2 out. then check if you really want to buy it. CS2 is basicly 7.0 but with more stuff on it so 7.0 is really like food and cs2 is like food with a topping.
hold shift, and clik on the layers you want linked, CS2 got rid of the chains, you can just select multiple layers at once. I like it. I have CS though, and what I said above is the only difference I can see. the difference between 7.0 and the CS series is smart imaging. and it helps lol.