Over the winter of '39-'40 the Soviet Union hurled its massive and incompetent military against the tiny but very skilled Finnish military. The Soviet aim: to move the border with Finland a bit further away from Leningrad.
The Finns exacted a very heavy toll on the Ruskies but ultimately their tiny force simply could not handle the flood of Red soldiers. This war seems largely forgotten in Western texts despite its part in the larger WW2.
One interesting potential consequence of the war had the West taken it more seriously in the beginning is that WW2 would have become a THREE way war with the Western allies vs Axis vs the Soviet Union as the Western powers were heavily against the Soviet invasion. However, the Western powers did not have much faith in Finland and waited to help. In the end, western aid was too little, too late. Had they reacted faster, Finland could have held out long enough that the West might have declared war on Russia (remember at this time Communism was a major threat to the west).
At any rate, here is a documentary I finally found on the subject:
Part 1
http://www.youtube.com/watch?v=1Qd5roKfgqoPart 2
http://www.youtube.com/watch?v=SCfo3eTn_lQPart 3
http://www.youtube.com/watch?v=VjfbJpZBi3YPart 4
http://www.youtube.com/watch?v=oucteCvrg6wTailwinds,
Adam