Set up their internet connection and put either a shortcut to the dial-up on the desktop or arrange their browser shortcut to dial upon opening. Save their password into their dial-up properties and put a note somewhere prominent on their monitor with their login and password. Now, the challenge is in explaining how to do all this stuff. Be prepared to explain and explain again and explain differently and then go over it again. Learning how to use a computer will be difficult for any newbie who has never used them before.
Patience is key.
Watch your verbage. Make sure you provide an easy definition for any term you'll be using. Avoid terms that are unnecessary for them to know. This is absolutely crucial. You may want to, at home, type up your directions and notes so that you can go back and revise as necessary and also so that you can print the directions up in a large, bold typeface and make them easy to follow.