The New York Times has a good summary of the military's case against CBS News. Essentially, the military wants access to the unaired portions of a video interview with one of the soldiers involved in the deaths of Iraqi civilians in Haditha during November of 2005.
CBS is claiming its first amendments rights to keep the footage unseen. The military is arguing that there may be footage that helps to incriminate the soldier and it should be seen by the court.
Obviously, the military is looking for a confession that the soldier may have given on tape. CBS is stuck in an awkward position. The soldier is clearly guilty, the only questions are how much guilt does he bear and how much can be proven. It's quite possible that CBS obtained an interview with the soldier only on the basis that it not air certain parts, and/or promises were made after-the-fact.
Regardless, CBS has claimed that isn't required to turn over it's excess footage because of its constitutionally guaranteed free press rights.
This footage is the equivalent of a print journalist's notes. In that it is information that was obtained from a source but not published.
Unfortunately, the US does not have a good history of protecting journalists, especially when the government is the opponent in a court of law. Yet, it is important for the government to recognize the necessity of the fourth estate (this administration does not, one example).
As much as the soldiers involved in the Haditha Massacre need to be punished, it is not okay for the military to subvert journalist's rights to get the evidence that they need.