This Method Mag Japan issue
is an awesome resource. There are two main options in Japan, Hokkaido which gets the most snow but the mountains are more like hills and the terrain a bit flatter. Then there's the Japanese Alps on Honshu (The main island) around Nagano where teh terrain is steepr and there's still a lot of snow. You'll probably fly into Tokyo, there are two airports there... from one of them you can fly direct to Hokkaido, from the other you'll need to switch airports. If you want to get to Nagano, you can hop on the Bullet Train. Best time to go is between Jan & Feb.