How can i travel from Tokyo to Hokkaido?

i'll be in Japan in Mar 2012. how can i travel from Tokyo to Hokkaido? What are the modes of transport available? Is air the only option?

I suggest you read through many of the helpful pages on japan-guide!

Usually each city in Hokkaido has an access page which can assist you on planning how to reach each destination. The following is for Sapporo which details the many different ways you can get to Sapporo.
http://www.japan-guide.com/e/e5306.html

There are many other options depending on where you wish to go in Hokkaido.

Do you know how long you plan to stay in Hokkaido?
Do you know which places you wish to visit in Hokkaido?
Do you plan on seeing anywhere else in Japan?
How long is your overall stay in Japan?

If you have time and don't mind spending it on trains then you can consider a JR Pass which will let you use the trains from Tokyo to Hokkaido, and around Hokkaido. If you don't have time then usually discount airfares are the best way, sometimes in combination with a rail pass.

This page lists a lot of the major sights in Hokkaido:-
http://www.japan-guide.com/list/e1101.html

Enjoy your trip!

The typical methods of transportation between Tokyo and Hokkaido are train or plane. Trains take considerably longer and tend to be more expensive (although a JR pass helps somewhat), but they can offer a more scenic trip especially if you have time to spare. Otherwise, air travel is generally faster and cheaper.