Mike Cohn has written an excellent article that covers a number of different options that can be taken when someone in an organization desires to implement an agile method. These Patterns of Agile Adoptions are described as three sets of contrasting options:
Here are my rough notes from the May 2005 Scrum Gathering in Boston. Regrettably I was not in the room for most of Mike Cohn’s presentation on User Stories… but his book (User Stories Applied : For Agile Software Development) is excellent 
The notes in this entry include predictions from Ken Schwaber, a presentation from Bob Schatz formerly of Primavera on their enterprise-wide implementation of Scrum, a panel discussion with Tim Bacon, Jeff McKenna, and Diana Larsen, moderated by Esther Derby. In the afternoon we heard from Pete Deemer about Yahoo!’s enterprise adoption of Scrum, Mike Cohn about User Stories, and to close the day we had an energetic presentation from Tim Dorsey of WildCard Systems about their enterprise implementation of Scrum.