II_billym, I do appreciate what you had in mind in your initial replies and I'm really not out to argue with you about this. The point I was making that the phrase I quoted from you was ambiguous to say the least and while the rest of us may have known what you were on about, amidacious might not.
I also understand that at face value, amidacious may not need to know why such an installation would not work. But here's a scenario: what if he/she was accustomed to installing programs via this method and can't understand why it doesn't work in Photoshop? How can you help the guy install it as you put it if it can't be done?
With reference to your second paragraph, it's plausible that the friend may have installed from a genuine CD. If he borrows that CD, it is possible to perform a second installation. The acquisition of setup files then becomes unnecesary. Perhaps his/her friend should be the first port of call.
Yes, you're right - the presence of "setup.exe" is sufficient to differentiate the setup files from the installed product folder BUT and this is a big but, it will only work with a modified cracked copy of the software. In fact it's easier in CS3 than in previous versions. Copying these files will not work. Try it yourself on another computer if you're in any doubt.
Although I spend my days finding software exploits, I'm not per se against file sharing as I consider much software grossly overpriced. Nevertheless, you've admitted yourself that you're using, let us say, an unofficial version. Like it or not, such versions do not behave precisely in the same manner during installation or use as genuine versions do and if his friend did have a genuine version, he's wasting his time.
Finally, I've got no objection to him/her "getting further" as you put it. I've already said what to do: download it via a torrent. That way as long as it's a good virus/spyware free version, it's sure to work