If you can't get PS, google The GIMP. Basically the best freeware program you can get that can do most of what PS can. Granted, PS is probably a bit better in some areas, but it's expensive--GIMP is free and has a lot of useful features.
I prefer easy programs so I use a combination of MS Paint and Game Maker's sprite editor. GM for gradients, color-changing, and rotations, Paint for everything else. It's limited but it works for my purposes. Haven't really done banners yet but I might get into that...