I upgraded to a 2GB RAM stick but now Photoshop is crashing even more. Almost everytime I open it, it freezes and I have to force it to quit 2 times before it actually starts to work.
Try reinstalling Photoshop, that may do the trick.
Have you more than one version installed?
Although I have CS2 and CS3 both installed on my Mac Pro without any problems, I've heard of others who have experienced problems when they had more than one version installed.