After reading healthservices post, I though this might be a good spot to post a little more info.
Here's the PelicanParts Tip service DIY:
Pelican Technical Article: Changing Boxster Automatic Transmission Fluid - 986 / 987
A ZF 5HP service video from ZF. Not the best video, because the fill port is apparently on the side of their demo model (BMW?), rather than the bottom:
https://www.youtube.com/watch?v=S8jcRd4gyWc
A better video, but on an Audi A4. It is pretty much identical to our version of the ZF 5HP19:
https://www.youtube.com/watch?v=uXil6QQOCmg
If you want to see an in-depth tear down of the transmission look for YouTube videos by "Jeff Richardson" (BMW version of the transmission)
Here's the manufacturer's parts catalog for the
Porsche 5HP-19 FL. It has some good diagrams and the fill procedure:
http://www.zf.com/media/media/document/int_print_catalogs_documents/usa_4/5hp19flporsche.pdf