The tricky part is selecting the head and hair, theres many ways of doing it, but some people find channel masks the way to go, a lot depends on image though, if you can post the shot here, somebody will probably be able to advise the best method of selecting it

Keith beat me to it.
whats wrong with tracing round it and deleting? took 3 mins
http://www.flickr.com/photos/48849701@N04/6365400675/in/photostream