I checked TV Guide.com - look at the posting for Entertainment Tonight - they specifically state: "Star Wars: Episode III: Revenge of the Sith" is discussed. Included: a look at it's poster. I also caught a quick ad for tonights show - and they state "never before seen, Star Wars Episode III info you won't want to miss". This is just like last time with the teaser poster. So looks like tonight is our first look at the new new poster!
Or ET could just be showing the preview of the trailer that Fox is showing on the OC commercials. They've been known to hype up Star Wars stuff like that many times in the past.
One time they hyped up exclusive Episode III footage and they just showed clips from a web doc that was MONTHS old.