Christine's Viking Movie Response

I thought the movie gave a great overview of the Vikings, but I was familiar with a fair amount of the facts the film presented.  One thing that I did find interesting was that the Vikings chose to convert to Christianity for the most part on their own.  However, since Norse mythology had such an important role in the lives of Vikings, I wonder how fully they accepted Christianity.  Could they have possibly only converted on the surface for political reasons while still holding on to their previous beliefs?  I feel like converting to such a drastically different religion so peacefully would need ulterior motives.