wat i mean about the 40% is mainly the processor and ram, i.e 40% of your processor speed is automatically taken up by vista alon, not the programs you might also be running, same thing w/ ram.
and about the CS3, xp can run it, but i would advice getting an external hard drive b/c pictures will eat up a 40 gig HD in a matter of weeks. and maybe upgradine your ram to a gig, this is pretty cheap probably $50-$60USD, go
here and scan your computer, it will tell you which kind of ram to get and how much it will cost.