While not very well armed, soldiers of Finnish Army were better trained, got used to fight especially deep forest terrain. Besides their arthillery got reputation of splendit fast and sharp fire. The defence was deep so the soviets couldn’t break it. Finnish pilots were excellent in dogfight, well organized and capable to execute modern type joint-fire operations with ground forces.

One more thing – reconnaissance of signal corps (radio) was very important. As early as 1942 they had managed to open to code of Soviet radio traffic so they were ready to gave information for troops of coming major breakthrough operations of Soviet forces.

Because the Finns could beat Soviet forces in Karelian Isthmus and Karelian Fronta and because Stalin and Stavka didn’t have enoug strategic reserve troops in that very import moment Finland was saved. Though Soviet Union never told the real numbers of their military losses their is were strong evidence that Leningrad Front lost about 130 000 – 140 000 soldiers dead, wounded, missing, captured during june-july 1944. Meretskov lost most likely some 80 000 soldiers.

Interesting piece of data. The official figures of losses from 5th of July to 31st of July of Leningrad Front in 40 129. However even when you use official figures of each units the figure is 58 125. That’s one example how unrealiable those soviet casualty numbers really. BTW – the most bloodiest stage of that battle was from 10th June to 6th of July. So those numbers of Leningrad Front came from time when the biggest combats were almost over coz soviets were short of men and tanks.

The volunteers in Waffen-SS Viking had nothing to do with the Winter War but the so called Continuation War that started on June 25, 1941 whith the russians once again attacking Finland.

Also, how was Winter War unrelated to WW2? If you think only the war between allies and axis was WW2 you are mistaken. Its as much related to WW2 as Polish and German war or the Chinese war with Japan. WW2 isn’t just one war, its timeline where whole world was pretty much fighting someone. And Winter War had some big part related in Soviets war machine, they realized how bad it was after the horrible war with Finns so when Germany came marching they weren’t completely ill-prepared.

Finland had volunteers in SS-Viking so it was not completely neutral, and German had some dealings with them before, we did join them against Soviets in Operation Barbarossa. The Finnish in SS did some awesome stuff also. Finnish were seen as elite soldiers so they got lot of very difficult missions cause of that.
http://en.wikipedia.org/wiki/Finnish_Volunteer_Battalion_of_the_Waffen-SS
Himmler – “Where a Finnish SS-man stood, enemy was always defeated.”