JAL oneworld, how to book

We are from the US, planning to visit Japan in April 2009 by JAL to Tokyo, and then travel from Tokyo to Osaka.
On the way back to Tokyo, I learn that we can book the discount ticket by JAL oneworld.
Do we have to book one way ticket from the USA or at the airport when we arrive to Narita airport?
And how far in advance to book that ticket?
Many thanks for your advise.

I guess you refer to the air passes. For more details and links to official websites, visit the following page:
http://www.japan-guide.com/e/e2364.html

Contact JAL in the US now if you have already booked the international segments.
You may be able to book the airpass portion now.

Contact #:
http://www.ar.jal.com/en/footer/contact.html

Airpass info:
http://gutereise09.blogspot.com/2008/07/japan-airpass.html

Hi Optimistk, Uji
Thanks for the link you posted. I called JAL already, they said I am eligible to book that oneworld airpass now or before I live for Japan, total amount around 15000 Yen.
Once again, thanks so much.
Merry Christmas and happy New Year