This is the bonus track from the Thyrfing's album 'Urkraft'. A cover of Gary Moore that is quite unlike Thyrfing's regular style :)
No, this is NOT Sonata Arctica. They have never made a cover of this song. However, the Nightwish version of the song features Tony Kakko, the singer of Sonata Arctica. That is probably the root of the confusion.
http://en.wikipedia.org/wiki/Urkraft
http://en.wikipedia.org/wiki/Over_the_Hills_and_Far_Away_(album)#Spinefarm_edition (link screwed up)
Also, I finally disabled comments, because no one is able to post any comments to this video that are of any relevance to anyone. They all follow the formula "Band/Version X is better than Bands/versions Z and Y". So please, find another outlet for those kind of discussions, I don't wish to be notified every time you guys decide to post how much better or worse this version is compared to the Nightwish or Gary Moore versions.