I would guess you're familiar with the Wacom Cintiq products? These are tools for photographers, designers, etc to draw directly on an LCD using touch sensitive pens? If not, you should look into them if you like working this way. These are tablet PCs so not open source, they're big, bulky, etc. But as hardware gets faster, smaller this may approach Nokia Tablet size.

(FWIW, I've never uses the Cintiqs. I used to be a pro photog and used the Intuos tablets. Once you get used to it I prefered drawing on the desktop and looking at the monitor - that way my hand was never in the way of the picture :-) )