I actually got one of those monoprice tablets
http://0.tqn.com/d/create/1/0/6/g/5/-/i ... es-001.JPG
they are around $50 and mine works really well!
As for animation programs, that's a little bit harder. I used to use Monkeyjam when I was on a PC. I THINK you can color your frames in GIMP then import them back into Monkeyjam to make animations (save the GIMP files as whatever file format Monkeyjam prefers, like TIF or JPG or whatever).
I am now on a mac so I can't run Monkeyjam anymore but another good one is Digicel Flipbook (
http://www.digicelinc.com/store.htm). Unfortunately that one's not free. It's somewhat cheap for an art program, and very versatile for animation but still kinda steep if you're a student or relying on parents to buy it for you.
As to animating by replacing the mouth, that is a very good way to save time and is sometimes called cutout animation. A lot of Flash Animators use this extensively with mouths and we usually have them all pre-drawn and ready to just drop in. Makes lip sync a lot faster!
Keep practicing! That's the main thing. The Richard Williams book is excellent. It may seem intimidating at first but take it a little bit at a time!
I also recommend Eric Goldberg's Character Animation Crash Course for more simplified, broken-down-into-steps instruction.
Good luck :D