Tablet is a tricky tool to use. It can't extend your abilities if you have none. Some talent for drawing is needed and even ppl that are good with traditional art tools struggle some time using the tablet. (like Bendover said)
I suggest for your first buy to be something that is not for professional use, cheap and small, so you get acquainted with the tool. Some of the Genius tablets would suffice because they give enough options for small price.
Forget Wacom for now. Too expensive, and you don't want to buy a nice, big, expensive coffee cup holder. XD
When I bought my first tablet I was sure that 'transfer' to new medium will be easy. I've rushed and bought a tablet that was in the 'almost pro' segment. Big size, good pen and good pressure ratio. Then when I've tried to draw stuff I noticed that my style and the way I do stuff doesn't go well with the new tool.
I got into situation where I was back to basics, with lines, with way of holding pen (angle that touch surface), the speed of strokes, the different way of drawing (looking at the screen and trying to get a 'feel' with hand on tablet etc).
It didn't work. So, a week later I was pissed because I just spent money on something that I thought I would use with ease.
Only my stubbornness and the awful feeling that I turned into donkey because of the rushed decision kept me going, trying, learning. And now I can't persuade myself to do traditional art anymore. So, it is a long process to accustom to tablet, even when you have worked with pen and paper years before. Keep that in mind.
Also, your style of drawing will suffer in the transition. Drawing on tablet is completely different than drawing on paper. You are kinda limited to 'let yourself go' and focus just on drawing. Lines are not going where you want them to go, control is not 100%, idk how to explain it... Some finesses just disappear when you work with tablet.
But, UNDO thingy is a blessing!