GIMPShop also
If it's the user interface the person has issue with, Gimpshop may be a better choice; I've not used it though so can't provide personal experience.
In the end, specialty programs will always dictate the platform though. If one can't live without Photoshop or AutoCAD specifically then they'll have to use the OS that those run on.
Now, first his old hardware, he could look at Xubuntu if he wanted to stick with the latest releases but use low resource hardware.