The G5 predated CS by a few months if you want to be scrupulously accurate. They became available in September ’03 (at least to the peope who ordered them in June), and Adobe announced the Creative Suite on 10/27/03.
And Apple was then out of stock of the G5 Duals by October ’03 due to the overwhelming rush of orders — although one of the mail-order houses had managed to stockpile some.
Photoshop CS (CS in general) requires OS X. And on occasion, I run PS/CS on a G3 iMac 500 DV/SE. Not supersized files — a tad too slow with a screen a tad too small. <vbg>