They're slate PCs and they're damn good.
In my experience, Motion doesn't skimp on hardware, is reliable as hell, and the external batteries will LAST - my little brother's old LE1600 still gets six hours of battery life off the primary and secondary batteries with everything on and cranked up to full (and Win7 Professional).
No matter what manufacturer you go with, I strongly urge that you go to Windows 7 for this - the handwriting support is worlds better than in Vista, and that was a hell of a leap from XP Tablet.
They are kinda expensive, though.
If all the world's economists were laid end to end, we wouldn't reach a conclusion. -- William Baumol