How Do I Activate Spaces In Mac OS X?
Spaces is available in Mac OS X Leopard and Snow Leopard. If you're using anything before OS X 10.5 you will not be able to use Spaces.
Spaces can be activated by going to the System Preferences and selecting Expose & Spaces. Click on the Spaces tab and select the checkbox that says "Enable Spaces". From there you can decide how many spaces to use, how to arrange them, and whether or not to show Spaces in your menu bar.