These are a series of introductory level videos which I highly recommend:
http://www.youtube.com/watch?v=6fs9wSF_GSQ
http://www.youtube.com/watch?v=E3xN0qmg3zI&NR=1
http://www.youtube.com/watch?v=OFaNYJGGTUg&feature=relmfu
http://www.youtube.com/watch?v=6UneWw5w890&NR=1