Im new ''making'' Graphics, but Paint.Net, a friend of mine suggested it, you got a better 1? if so teach me ''Real'' Graphics? I also only used 1 layer.
You should definitely download PhotoShop, if you go on www.thepiratebay.org and search "cs4 micro", there's a 50mb one by kentuckykid, installs in a minute.
As for the graphics, they're very good for your first graphics, keep it up.