[Harp-L] During practice - Play along with that tune .. Keys?

[Mw Fitz <tidewalk@xxxxxxxxxxx>]

This has probably been asked and answered a good many times before? Anyway, since I'm new here I
thought I would ask. Say I hear some tune being played and I want to play along. How do
I find out what key they are playing in? Thank You! Just a song for an example.
http://www.youtube.com/watch?v=Qerg0LyLi6c&feature=fvst