There are several technical solutions for those who cannothandle a mouse. Voice control is one. There are also special interface software packages which let the user run things with just one giant button (for those with range of motion difficulties), or a single switch that they activate by puffing on a tube or nodding their head.
I have also seen a pointing device that consists of a simple reflecting disk that is stuck to the forehead, which reflects a laser beam (very low power) back at the screen so that simple head movements control where the beam lands, combined with a switch of whichever design is workable for the individual. All of these and other devices designed to provide computer capabilities for people with various physical constraints have been around for years and are known to special ed people -- they have a whole industry. But they don't get sold through mainstream computer outlets, needless to say.
Here are some starting points for researching what is out there and where:
SERI Special Needs and Technology Resources
...SERI Special Needs and Technology Resources Closing The Gap - is ...of microcomputer technology in special education and rehabilitation....
DREAMMS ... Links to Special Needs Web Locations
... Special Needs Web Destinations Topic Searches Educational ...Publishing Henter-Joyce IBM Special Needs Information Children's...
Special Needs Computing
... Special Needs Computing Articles How Apple II Computers...
NISS - Special Needs/ Disabilities
...aspects of computing for people with special needs ... Special Needs/ Disabilities Sites specifically for those with, or...