A Wacom stylus would help considerably. I'm biased, however -- if you check my signature, you'll see that I still own a proper tablet PC. Most graphic designers just use a Wacom Intuos tablet. It has the advantage of not covering your drawing with your hand or fingers. It's also much more precise, and you can use it with a large 27" or 30" screen. LCD tablet combos are usually small, they get very hot to the hand after even a short period of use, and you can actually see the reflection of the ceiling lights on the device.
Give me Photoshop, a stylus, and a good note taking application similar to Microsoft OneNote, and I'll buy an iPad immediately.