由東京成田機場轉機到北海道要先清關, 那可以到外面走走嗎??

全部正確，JR在機場有 tourists center，可以買rail pass。

2007-07-30 17:40:56 補充：
如果唔駛清關，你在香港機場會出兩張 boarding pass，一張香港-成田，另一張成田-札幌新千歲。但如要清關，你在香港機場只會出一張香港-成田 boarding pass。

2007-07-31 09:17:44 補充：
大家有所不知，成田有機去札幌，而成田並不是純國際機場。

2007-07-31 13:43:06 補充：
￥10,000的JR East Pass 仲有。並不限量。http://www.jreast.co.jp/tc/eastpass_sp/index.html

I just returned from Tokyo yesterday. But the counter staff of JR ticket office said the promotion of 10000 yen for East Rail Pass has expired. We had to buy it at original price at around 28000 yen.

If you are going to Hokkaido and need to change at Narita Airport (成田) in Tokyo, you have to travel and go to another domestic/ local airport (羽田) by shuttle bus or train. You cannot just stay at Narita airport because it is for international flight only. It's quite far away and you cannot just walk. Make sure that you have enough time to go from one airport to the other. The luggage will be handled by airlines and you need not carry it.

And you can buy JR pass when you check out from Narita airport. The counter is near the exit. Then travel by shuttle bus or train to domestic airport.

Hope I can help! Enjoy your trip!