The WSJ has a great article today (paid link only) on the HP "pretexting" fiasco. The article covers the background and timeline of the events, but reading between the lines I think one thing is clear: this was an example of office politics played at the highest level.
Board Member Tom Perkins used his influence to point Chairman Dunn down the path of squashing board leaks. Once the hook was in, he worked to set it in deeper by tacitly encouraging it, leading Dunn to believe that it would settle internal board strife. Once Dunn ran out a good length of line overextending herself, he reeled in the catch by exposing the breadth of the investigation, not only forcing Dunn off the board, but ruining her reputation and getting her indicted.
Dunn is ultimately responsible for her own actions, but Perkins was behind the scene, setting up the stage for Dunn's self-immolation. This episode will probably be turned into a book on business ethics, but what it should be is a case study in Machiavellian plotting.