The biggest obstacle that I have seen for epople who have no exerpience working with computers is the operation of the mouse. Keyboard is no problem; it's just like a typewriter. And even using windows is OK, a reasonably clever person will start by memorizing things by rote and then will start figuring out the metaphor of "folders" on a "desktop", etc. The mouse though is very tough, aunt found that even though her hands don't shake and she does needlework requiring much finer motor control than a computer mouse, connecting the 2d horizontal motion of the mouse with the 2d vertical motion on the screen was much too difficult.
The iPad, of course, solves this by using a touch screen. Want to open something? Touch it!