This page explains step-by-step how to make the mouse left-handed in Mac OS X. Unless you have a single-button mouse, your mouse is set up for a right-handed person by default, with the primary button on the left. However, you can swap the function of the mouse buttons from the default left click, so that a right click is instead used for selection and dragging. You'll just need to remember to press the opposite button to what is called for when you are following instructions (for example, if you are requested to right-click on something).
Step 1: Open the 'Keyboard & Mouse' window
Make sure you are in "Finder." If necessary, press Apple+Tab to cycle through the open applications until you return to "Finder."
Click on the "Apple" icon on the menu bar or press Ctrl+F2.
Click on "System Preferences," as shown in fig. 1, or press the down arrow key to highlight it and then press Enter.
In the "System Preferences" window (shown in fig. 2), click on the "Keyboard & Mouse" icon, or press Tab repeatedly (you might need to press Ctrl+F7 first) to cycle through the icons until the "Keyboard & Mouse" icon is highlighted and then press the Spacebar.
Step 2: Swap the primary and secondary mouse buttons
In the "Keyboard & Mouse" window, make sure the "Mouse" tab is selected. If it is not, click on it, or press Ctrl+F7 to highlight one of the tabs and then press the left or right arrow key to select it. Depending on the mouse you are using, you will see something like the window shown in fig. 3, which shows the default button settings for a right-handed person.