I think I figured out how to upgrade to Photoshop CS3 from Photoshop 4 (with 5 upgrade). On there site, it says only Photoshop 7 and up can upgrade, but CS2 can upgrade from any version.
So I was going to buy CS2 and run it on my new Mac Pro, but then read about "Free CS3 upgrades" and since I will purchase CS2 upgrade after CS3 was announced, I should be able to get Photoshop CS3 upgrade for free.
Did I beat Adobe on this one? Also reason for not upgrading, money, no need to etc.