What are you going to be using Photoshop for? I have found that with my upgrade to CS that it really hasn't made that much of difference from 7.0. I mostly use Photoshop to adjust the color balance and sharpness of my pictures. I have done some picture manipulations, but it takes forever and if your not proficent(sp?) with it you waste hours on end trying to work with the program.
I say save the cost of the upgrade to CS and just get 7.0. It is a very powerful tool and you can install it on as many computers as you want. With CS, you only have the ability to install it on two computers which is a p.i.t.a. if you're like me and have three or more computers that need the program.
-good luck