Russell Koenig describes how he customized his mouse buttons for use in AutoCAD.

"It’s almost impossible to be an efficient CAD user without a mouse that has left-click, right-click, and wheel functions. I prefer a mouse that also has left and right side buttons. I’ve assigned the button by my thumb to be the keystroke Ctrl+[ , which AutoCAD understands as Escape or Cancel, and the button by my ring finger to Ctrl+Z, which is Undo. It feels a little strange at first, but you’ll find that it becomes second nature before long."

Notes from Cadalyst Tip Reviewer Brian Benton: Five-button mice can save you a lot of time. There are several ways to customize them. Many such mice come with software that allows you to customize their buttons in any program you are using. That will work just fine, typically. You can also customize mouse buttons in AutoCAD. Open the CUI (Customize User Interface) Editor and go to the Mouse Buttons section. There you can customize your click, Shift+click, Ctrl+click, and Ctrl+Shift+click options.