Microsoft Corp. first talked about the auxiliary display concept at the Windows Hardware Engineering conference in 2004. And Intel Corp. showed a prototype of a device with an auxiliary display affixed to a laptop lid at its Intel Developer Forum conference last fall.More info at eWeek
Longhorn to support auxiliary displays

Microsoft disclosed that the beta version of Longhorn will include support for "auxiliary displays". Auxiliary displays may come in many forms; such as displays attachted or build into laptops or software add-ons to cell phones, PDAs, TVs and other devices.