I would advice against Tablet PCs (that's the name for what you're looking for) for several reasons, they're okay at doing multiple things but not Great at anything.
Cons: -If it has touch it often produces a grainy effect on the screen. Also touch costs a lot extra (100+ dollars). -They're rarely over 11" making them super uncomfortable and small. -If they have a Wacom pen it doesn't do tilt or go above 512 levels of sensitivity. Btw, do not get ones that do not use Wacom as they often don't work with popular software. I'm not sure what the other major brand was that supplied digitizers was called, but they didn't support photoshop for years. -They're not very powerful and have mobile cpus and integrated graphics. -Even if they claim 10 hours it's probably like 3, maybe. I had one that claimed 7 and it only lasted 2. Thicker batteries barely add any life and stick out the back. -No Button Shortcuts! This drove me crazy and I programmed a numpad to do shortcuts. -Most new sleek tablets do not have pressure sensitive pens and if they do (Samsung Galaxy Note) they're not powerful enough for serious work. -Good ones are expensive (1000+ new, 700+ refurbished/used). Bad ones are cheaper but made of plastic and heat up like crazy. -Bad Color accuracy although this is true of 99% of laptops unless you get it custom made with a special screen. Desktop monitors tend to have better color accuracy than laptops though and it's easier to change the screen. I'm not sure what you use now.
After owning 2 because I thought I couldn't stand not having the pen on the screen, I finally took the risk and replaced my tablet pc with a gaming laptop (with a 95% color accurate Full HD screen) and an Intuos 5 and I'd never go back. In fact, I used my Intuos at first with an old desktop because my laptop hadn't arrived and it worked fine. The desktop was a bit slow with bigger paintings but the tablet worked marvelously.
Pros: -I miss being able to rotate the screen to show people things. -I'd add portability but between the numpad, the mouse, the charger, and the pen, oh and often headphones, it was a mess. A few more pounds, one more thing (the intuos) wasn't going to make much of a difference. I took out useless stuff and got a bigger backpack. I always carried around a bunch of stuff anyway. Also the battery usually doesn't last enough on tablet pcs to enjoy the portability. I'd take it to school and two classes later it would be dead.
FYI, trying to use a touch screen for drawing isn't as good as using a drawing tablet. It's harder to work with because your finger covers the area you're drawing on and they lack pressure sensitivity. It's basically the same as using a mouse, but you can't see what you've done until you lift your finger.
Some tablet PC:s have pens available that support pressure sensitivity. I'd say the best of them are probably about Bamboo quality when it comes to drawing. And the ability to draw on the screen is definitely a plus.