How to Change Mac OS X Snow Leopard’s Screen Saver
Customized screen savers are popular, and Mac OS X Snow Leopard offers you plenty to choose from in System Preferences when you click the Desktop & Screen Saver icon and then click the Screen Saver tab. You can also download and use third-party screensavers.
To add a third-party screen saver module so that everyone can use it on a multiuser system, copy it into the Screen Savers folder within the top-level Library folder. To keep that saver all to yourself, copy it into your user account’s Screen Savers folder (which is located within the Library folder in your Home folder).
Click one of the entries in the Screen Savers column to display a thumbnail of the effect. Selecting the Use Random Screen Saver check box runs through them all. You can also test the appearance of the saver module by clicking the Test button; the screen saver runs until you move the mouse or press a key.
To keep tabs on the current time, click the Show with Clock check box to select it. Snow Leopard adds a clock display to any screen saver.
Many screen savers allow you to monkey with their settings. If the Options button is enabled (not grayed out), click it to see how you can change the effects.