Have you thought about a Mac Mini or a XP PC sized equivalent? Depending on how much dexterity your parents have with their hands, a full sized keyboard and mouse will probably be easier for them to use.
Also, the high resolution screens that laptops have may not be the easiet thing for them to see. They might find a 17 or even 19 inch crt running 1024x768 a lot easier to use (I know my Dad does). Although size could be a problem for you.
Anyways, just some things to consider...good luck with your search.
-KeithP