I highly recommend the Open Source version-- the Gimp.
This is one of the best written pieces of software (in either the open source, or commerical worlds). There is plenty of documentation both in the program and online.
I use the Gimp professionally (I occasionally need images when my work calls for web page images).
You can get it, without strings, for free. Don't waste a single dollar on that other program.
http://www.gimp.org/