Tablets are overrated. Typing is much faster and accurate than handwriting; the only benefit you get are the ability to do doodles and illustrations, something you can do with a portable Wacom you plug-in as needed.
With laptops, I find lugging around, finding space for and plugging/unplugging a mouse to be a huge hassle. A wacom would be even worse. Also you can write with one hand which is infinitely better than typing with one hand. When doing research that's a big plus.
I'd say get one of those tablet EEE PC's. They're under $1K, have USB and bluetooth, and run full Windows 7. I have no idea how accurate they are though.