iPhoto stores its photos in a Package type thing. Its located in your user folder under Pictures/iPhoto Library.
To get your pictures out, right click on iPhoto Library and click "Show Package Contents" and go to the folder "Originals". All your photos should be stored there.
Make sure you only copy the Photos from there. Don't mess with the content of the Package, if you do I can't predict what will happen to iPhoto and your library.