Hmm.... personally, I don't really think you're ready for a tablet yet, but it's your choice.
(off-topic: btw, even though I'm a mouse-user. I also have a 12 inch tablet for some tasks that just go much faster with it. Most of the time though, my niece finds it pretty entertaining http://www.facebook.com/photo.php?pid=6 ... 1047137391
edit: Ya know, when I recommended using the mouse for digital art, I didn't mean literally using it to draw.
I'd say you need to learn some proper drawing techniques. Your sketches indicate that your hand isn't accustomed to using the pencil for drawing. You're making pretty long unbroken lines, which might be because you're trying to make your drawing look neat?
Here's a basic tutorial: http://drawsketch.about.com/od/learntod ... todraw.htm
It's not the only way to draw, but it's a good overview of the techniques you might want to start practicing.