Rail Reservationns 12/21 - 1/3

Are there travel agencies that will reserve rail tickets in advance? We will be traveling to Japan during the peak season, and I have little doubt that no seats will be available by the time we get there.

Also, we are on the fence regarding the rail passes. Does anyone think it makes sense to purchase 7-day or 14-day passes with the following itinerary:

12/21 - arrive Tokyo
12/24 - depart Tokyo
12/24 - arrive Sapporo (via air)
12/27 - depart Sapporo (via sleeper train)
12/28 - arrive Kyoto
12/29 to 1/2 includes day trips to Hiroshima, Miyajima
1/3 - depart Kyoto
1/3 - arrive Tokyo Airport(and leave Japan)

Thanks!

This new? company offers train reservations for tourists: http://www.jet-lag.org/en/jr/jrtickets.html
A7 day JR Rail Pass starting 27. Dec. does not cover the Kyoto - Tokyo return as it expires 02. Jan. A 14 day JR Pass covers all days and the Yen 16800 higher cost is somewhat equal to Narita airport - Tokyo, Kyoto - Tokyo and Tokyo - Narita airport by single tickets. But does not include the ( night ) Twilight Express from Sapporo to Kyoto. With the 14 day JR Rail Pass you can only go from Sapporo to Aomori by JR day trains, Aomori - Ueno by JR Akebono night train, Ueno - Tokyo by JR, Tokyo Kyoto by hikari shinkansen. This means arrival Kyoto 10.30 h or later next day