The Times (UK) has the best, most detailed picture of the Clinton attack strategy against Obama and definition of "swiftboating" you'll see anywhere:

Swiftboating" has become a metaphor for attacking a candidate's strengths head-on, instead of their weaknesses. In Obama's case, it means calling into question his multilayered racial and religious background and his reputation for scrupulous integrity. The smear that Obama is secretly a Muslim, or too close for comfort to that religion, has already taken hold among some voters. [/quote]