In that case, perhaps you should look into Paint.NET. I've used it before, it's just about the best free thing and comes close to Photoshop.
I don't know what to put here right now.
But....you just said Windows is set...oh wait I totally misinterpreted what that means didn't I?
I don't know what to put here right now.
GIMP basically is just another company's version of Photoshop. They do almost all the same things- just with the buttons in different places. It's like comparing McDonald's to Burger King. People will have their preference but when you get down to it they all have the same stuff.
So yeah, both GIMP and Photoshop should work for you. People usually say GIMP is the free one while Photoshop costs money (which is true I guess) but I could get you a free Photoshop download with ease. Most can.