In my opinion - backed by some research, invasion of Finland was just the Soviet attempt to grab the territory that was "allocated" to them according to 1939 Molotov-Ribbentrop theaty.
Russians already had the "people" finnish government ready to be imported and assume the puppet rule.
Allies certainly did something about Poland - french valliantly declared desperate war on Germany they have no hope of winning - especially since their ally England concentrated it's efforts on protecting themselves from superficial damage by keeping essential modern fighters home and sending too few troops to the continent. The US of course did not even think of coming to it's historical friend and enemy help long after it was defeated and Hitler actually declared war on US.
Still, failure to defend/liberate Poland on the part of France and England does not negate their attempt to do so.
Also, there is a huge misconception about the relative size of the USSR and finnish forces. While USSR had "5,700,000" troops in it's whole army - incuding millions in the Far East, the logictics of the situation - the layout of railroads, remoteness of the terminals from the front, number and quality of the roads, few meters of snow cover, etc. - would not have permitted to operate more that just a few divisions altogether - few tens of thousands people.
If it takes more fuel to burn to get there than a car can carry certain distance from the railroad, your operations effectively end at that point. Adding more troops than your ligistics can effectively support causes reduction rather than increase in the combat power.
Taking prepared positions (20 years of building on the part of brilliant and prophetical Mannerheim) in severe winter conditions with meters of snow cover, limited roands against well-prepared and motivated enemy was quite a feat on russians' part - due mostly to terror of troops of their officers more than death or cold or starvation.
It was lucky that finns resisted as long as they did to make Stalin stop and postpone his plans to occupy their country. They could have gotten it back eventually but their intellectual elite, officers, teachers, priests and buisness class would have been exterminated just like those of Poland and baltic countries.
miko