Will not have a rental car in Greece so we will be relying on busses & trains for our transportation needs. Is there a website(s) that shows train schedules? If this is too vague, I'm mainly interested in transportation between Athens airport & Olympia.

Hi

See - http://www.ose.gr/echome.asp?lang=2#. From what I can make out you take a train From Athina to Pirgos then from there a train to Olimpia. Check out the timetable on the right hand side to tee it all up. This site might help too - http://athensguide.com/schedules/trains.html

The Greek railways are in the middle of a big modernisation programme. The line from Athens to the Peloponnese was a narrow gauge line, but is being replaced by a new, faster, standard gauge line.
Currently, you need to change trains at a new station outside Korinthos. New suburban trains run from Athens airport to Korinthos (www.proastiakos.gr but only in Greek). At Korinthos, you change to a narrow gauge train which is waiting on the other side of the same platform. The Proastiakos trains run from the airport to Korinthos every two hours, but not all have onward connections towards Olympia.

"(www.proastiakos.gr but only in Greek"

But if you click on the icon on the left with the photo of a train, you get a schedule in Greek and English. It's one of those yucky pdf files though.

Thank you!