Photoshop CS3 performance

I've been running CS3 for a while now, but I'm pretty disappointed with it's performance compared to CS2. It seems slow and "sticky" (esp. with type and marquee tools) and the display is rough looking and pixelated.
Anybody else get this? I'm considering re-installing CS2.

Any tips to optimize it? It only seems to have found half my RAM. How can I make it use all 6GB?

I'm running a Mac Pro, 2x2.66, 10.4.11, 6GB RAM, NVIDIA GeForce 7300GT 256MB.

Sure you haven't got it running under Rosetta?

In a word, no. How would I find out?