I'd go with the GIMP. Inkscape, Sodipodi and XaraXtreme are vector-graphics programs, which isn't a bad thing in itself but they don't seem to be what you want at the moment. Artweaver and paint.net both look like watered down photoshop clones so I wouldn't go with either of them (and I strongly dislike closed-source). For really flashy 3d effects you could try downloading
Blender3d, but then you would have to learn how to model which takes quite some time.
Should you decide to try out GIMP I'd recommend
Gimptalk for forum and tutorials.
Why would I want illegal bootlegged stuff?
Because it's cool to be a software-pirate and you can get expensive progs for free.</joke>