There must be someone around here that knows GIMP well enough, surely...
I was looking into this myself just recently.. Im a n00b when it comes to image manipulation. I found hopping straight into Photoshop is an expensive and perhaps daunting way to go about it...
I am having a great time using the wonderful and free paint.net
and making my way through the beginner tutes and how to's...
about backgrounds, cutting and transperency are the most commonly used.
Im glad there are things like paint.net and GIMP
around.. by the people, for the people y'all !