If you are proficient in both Macintosh and PC, you should offer training in both types of computers.
You could probably make a living helping seniors learn how to use the internet and e-mail to keep in touch with their loved ones, who are now commonly spread around the country.
Err on the side of caution in this business. People do not want to know all the details about what makes a computer work.
If you overload them with information from the beginning by explaining bits, bytes, and megapixels, they will stick to their paper and pencil forever.
Photo by davidlat.