One difference is that Paint Shop Pro is available as shareware, while Photoshop is a commercial product. Well, I'm glad to hear that you think that. If you'd like to help, first of all, please visit my sponsors above. Second, spread the word to your friends and neighbours. Third, if you wish to link to my site, feel free.
Full instructions are available on the links page.
That's about it. P.S. Don't forget to add this site to your favorites for future reference.