http://www.youtube.com/watch?v=t0WQzTqNE4k&feature=related
This is my favorite version on YouTube because the sheet music is shown which makes it easy to follow and to listen to each individual part.
This is performed in a traditional manner.. It is customary for the choir to sing a line and then pause while the organ plays a musical response. The choir sings again and the organ responds. This pattern repeats generating a musical conversation.