transportation from Narita Express

I will arrive at Narita Airport Terminal 2 at 20:30 on July 12,2008 and stay for 9 days. I understand that the last NEX train leaves at 21:45, the SOBU rapid line leaves at 22:16, the Keisei Skyliner at 22:02 and the limited express at 22:42. Upon arrival ,I still have to exchange for JR Pass and also to buy train tickets into Tokyo . Only after that will I know which train I can catch but these trains only have reserved seats. Does this mean that I cannot buy the train tickets right at the airport? How far in advance do I have to reserve the seats? Can the reservation be done from overseas? What should I do?
thank you all for whatever advice you can give.

Confused,

Reservations are required for the Narita Express and Keisei Skyliner, but seats can be reserved at the same time as you buy tickets (or when you exchange your voucher for Japan Rail Pass). As has been mentioned numerous times here before, you can usually get seats up until a few minutes before the time of departure, except at busy times. If you are using the Narita Express from Tokyo to Narita Airport when you leave, you should reserve seats several days in advance, as these trains fill up more quickly (since people know in advance what time they will be travelling).