Everyone is going to tell you that turning your 650 into a snowbike is a waste of time, and that its a big heavy pig, etc. The truth is, there are better bikes to start with.
But your 650 is a big torquey beast and it would make a cool project. I love those bikes. If its your 650 or nothing, then I think you should do it.
Fitting a track to a bike is not rocket science. I'm sure I remember some guy out there who has done this.
I would like to hear how it works out, if you can make it happen!