so.....not many know that MAC is centered around the FreeBSD kernel........
Tell you what you can do.........Download the LiveCD from http://www.ubuntu.com/
You can download GIMP, which is a very similar design tool akin to PhotoShop.............It is by no means CS3, but it is very functional.........
Keep in mind, running from the CD, your experience will be depreciated as the CD's transfer speed is no where near the transfer speed of the hard disk.........but you will have an idea.
I would advise to wait until the new relase of Ubuntu in 7 days.........it is much improved......
Also, join the forums and ask your questions.
http://ubuntuforums.org/
The benefit is FREE to download, FREE to install on as many systems as you wish, FREE to share and if you are so inclined to do so, it is FREE to be changed so long as you share your changes with the community. Most software is also free.....there are many versions you can buy, I believe that Photo shop will have a Linux release shortly.