After having a quick glance at Photoshop CS3 there doesn’t appear to be any major changes from CS2 (well apart from it actually working fully in Vista unlike CS2 and a slight layout change).
The only change I could find is when you open certain vector format files (ai/eps) that give you the PDF import box (click the number 6), CS3 gives you the ability to specific the size of the image – show adjust the max. Dimension to 800 pixels and ensure Constrain Proportions is ticked as below: