I don't know the finer differences between the ps2 and the ps3 versions, but I'd guess ps2 will be more of the same, while ps3 will be more of the same but looking better and with diving.
For real now, ps3 has gameplay improvements over the ps2 version that you'll not be able to enjoy, such as the better player control and such. About specific things like short and long passing, shooting, etc., I'm sure they'll be tweaked for the new ps2 version, but I'm also sure they can't be the same as in ps3 because the engine is now quite different. Current gen and next gen are two different versions, not just the same with different graphics.
In my personal opinion, and I know some people will differ, you'd not be missing a lot if you postponed the upgrade until PES 2009. I bet the game will truly be much different than the ps2 offering at that point. If there is a ps2 offering, that is.