I would argue that Gimp is a resaonable match for Photoshop in terms of ability, but perhaps not in terms of usability, though I haven't tried the Windows version. Gimp will do the job you want, but it can be confusing and non-intuitive, although I find Photoshop confusing sometimes because I'm less familiar with it. The main thing going for Gimp is its price: free. (Oh, and you get to feel all warm and glowing because you're supporting open source development.)