Overnight train Tokyo to Sapporo

We would like to travel via Hokutosei No.1 overnight train from Tokyo to Sapporo on 28th Jan 2008 & return on Feb 8th 2008. We understand we cannot book this train until we arrive in Japan mid-January. Due to the snow festival in Sapporo is it likely that the train will be booked out at this time?

You may be able to reserve seats before you leave from your country.
check URL ... http://www.japanrailpass.net/eng/en003.html

Unfortunately, overnight train is not popular in Japan recently, because of expensive fare and taking long time... But I recommend you to book in advance.

And do not forget to book your accommodation in Sapporo. This season is high peek, very hard to look for accommodation. When I made business trip in this season, I was hard to look for it. Take care because Hokkaido in winter is very cold...

Look at alternates such as domestic flights, if you find a deal it probably comes out to as much or cheaper then getting onboard and paying the extra suppliment for an overnight train to Sapporo, plus its a lot faster.

http://www.japan-guide.com/e/e5306.html

You may be able to reserve seats before you leave from your country.

I am afraid, there is usually no way to make bookings from outside of Japan, unless you have a friend or agent in Japan, who can do it for you.

...and your accommodation
Unfortunately, overnight train is not popular in Japan recently, because of expensive fare and taking long time...

It depends on the train! Overnight trains to Hokkaido remain popular, especially the luxurious Cassiopeia. There is a risk that the trains will be sold out, especially on the Friday evening of the snow festival (in direction of Sapporo) and possibly Sunday evening in the opposite direction. Possibly on other days, too.

If you have the money and luck to make a reservation on the Cassiopeia, I can highly recommend it:
http://www.japan-guide.com/blog/schauwecker/070227.html

Thank you all for your help!