Use Spotlight to search for Automator.
Select File + New + Application.
In the search window type "ask for finder items. Drag to the workflow stage.
It should like this. Check "Allow multiple selection." (This is very important)
Clear search window. On the left, click on "Presentation," and then "Create PowerPoint slideshow." Drag that item to the stage.
Go to "File" and save Automator file to your desktop.
Open the Automator file.
Locate the photos you would like to import into PowerPoint (for a shortcut use Command +A to select all).
A PowerPoint slideshow presentation will be generated automatically.
For an easy way using iPhoto, open PowerPoint, and select the "scroll" icon next to "Window" on the menu bar. Select "Sample Automator" and "Create and run a presentation using images from iPhoto."