PEF is Pentax' (Pentax's? What' s the posessive of something ending with "X", anyway?) proprietary RAW format. That means that it may or may not be as available as DNG, which is an Adobe standard, much like PDF is.
What I'm driving at is that since PEF is proprietary, it's possible that iPhoto simply can't read PEF. I'm (unfortunately!
) not a Mac user, so I can't be of any more help. Sorry.