Were you hoping, for whatever reason, that some sort of HDMI cable might be released for the current Xbox 360 core and premium versions? Well keep it hoping, because it doesn't look like it's coming.
Posting on his blog, Ozymandias, who works for Microsoft, responsed to a question asking whether there will be a HDMI cable released for early adopters of the Xbox 360.
Unfortunately there will not be an HDMI adapter released for the original 360. The HDMI spec is basically a 2-way street and requires the specific port on both sides to be enabled. This is why we had to change the box.
If anything is to be released, it will probably be an analog to digital converter, which would kind of defeat the purpose of getting HDMI in the first place!
Source: PlanetXbox360