Photoshop isn't cheating, and GIMP has many of the same tools as photoshop.
I do a lot of painting and drawing in photoshop (see the armatars I submitted this month), those were all done with drawing skills. I don't think it's fair to say that using photoshop is 'cheating'.
Not everyone can afford photoshop, which means that those who do own it are given an unfair advantage. Thus, using photoshop is against the rules to level the playing feild.
Why are you so desperate to change the rules? Wouldn't it just be easier to abide by them over fighting them?
And I have never used gimp, but I am assuming that it does not allow multiple layers to be made. I suggest just dealing with it instead of causing commotion, its the best way to go when new to the forums.