We have used some of site in our computer classes:                                               

Welcome to Mousercise
http://www.3street.org/mouse/
A fun little application that will help you learn mouse skills.

Mouse Exercises
http://www.seniornet.org/howto/mouseexercises/mousepractice.html
Here are some simple exercises to help you get aquainted with your new best friend -- the mouse.

Learning Ladder: Using the Mouse
http://learningladder.org/basics/part1.htm
This site has a good basic overview of the functions of the mouse.