You may want to take a look at this thread
Also this thread
"There are some incompatibilities, and I personally would not update if I were in your situation. PS 5.5 works, but will always crash if you use the File Info. (A good way to lose all your work up to that point - save you're work often!). So far, it seems to work otherwise, although when I quit the program, it closes down very quickly and about a minute latter a notice comes up that PS shut down unexpectedly. It did freeze the computer once. Also, if you quit the program, it will not ask you if you wish to save the changes."