CS3 is still so new that CS4 isn't really on the horizon, and even if it was, CS4
will not be 64-bit for Mac, anyway.
When the release of CS4 becomes imminent, Adobe will start offering free upgrades to those who buy CS3 in the last 3 months or so before the release (at least that's what they did this time around).
CS3 Design Premium is a fantastic set of applications and are well worth the price, if you can afford it.
Not so fast. InDesign is pretty much a must-have for anyone doing print work, and Acrobat does wonderful things, as well. Besides, the price for buying just Photoshop and Illustrator nearly exceeds that of buying the whole Suite.