this must mean that it will work as external for any source...
"In a clever touch, the 27-inch iMac has a new feature that dramatically increases its versatility. Via a series of adapters Apple says will be available shortly, users will be able to attach external display sources, such a DVD players or even other computers, to the iMacs display. At that point, those sources will take over the iMacs display, effectively turning it into an external monitor or an HDTV."
"In a clever touch, the 27-inch iMac has a new feature that dramatically increases its versatility. Via a series of adapters Apple says will be available shortly, users will be able to attach external display sources, such a DVD players or even other computers, to the iMacs display. At that point, those sources will take over the iMacs display, effectively turning it into an external monitor or an HDTV."
http://www.macworld.com/article/143394/2009/10/imac.html
He notes 2/3 through the article about the inputs and specifically states the adapters are needed and they will support items such as DVD Players.