When previews are enabled, the Special menu lets you view all the pictures contained in a folder or smart folder as a slideshow.
Select any of the folder's pictures in the Special menu and choose Slideshow.
During the slideshow, use the controls at the bottom of the screen to pause and resume the slideshow, move forward and back through pictures, view an index of all pictures, zoom in pictures to fit the screen, and add pictures to your iPhoto library.
When viewing the index, you can see file names by moving the pointer over thumbnails and view a particular picture by clicking its thumbnail.
To end the slideshow, click the Close control or press Escape.