Touchscreen MacBook conversions aren't new, and in fact if you've got the money then we'll be the first to say that the Axiotron ModBook is a great off-the-shelf OS X tablet. If, though, you don't have the money and you want the accuracy of a Wacom active digitizer, you might have to replicate Wei's iTab project: merging a Wacom Intuos tablet with a first-gen 1.83GHz MacBook.
Video demo after the cut
The MacBook donated its working internals, but not a screen - that was damaged - so a replacement LCD was sandwiched in-between it and the Intuos digitizer fascia. The optical drive still works, and the ports have been re-routed to a new side panel; there's only one available USB, though, as the second is used for a permanent hook-up to the digitizer.
There are some nifty design touches, too, such as using the broken display's magnets to hold on an Apple Remote. The whole thing apparently cost less than a brand-new low end MacBook (thus far below what Axiotron would charge for a Modbook).