Like Meldrew has said, just copying the files won't put anything into the registry, so the computer won't have a clue as to file locations, associations, permissions, or any of the other codes it needs to run. Most programs will need something in Registry to work
Paintshop Pro 8 does seem to work with just a straight-forward folder copy as I found last time I had to fix my machine, but I'd be very surprised if anything Adobe released didn't fill the registry with gunk and junk.
I'm in the same boat as you Spotty with regards to Photoshop, so its back to Paintshop for me when I get my computer back up and running (its feeling very sorry for itself at the mo and has decided to stop playing ball!)
Glen