Don't really know of any download programs...with the exception of Gimp. Which i haven't used personally....but believe that it is quite a good program to start with.
Photoshop is the best on offer IMO. And that is what you should try for...even though it is very expensive. The next best...probably Paintshop pro...thats pretty good...and i do occasionally still use that.
Hope this helps a little - look forward to seeing what you come up with