Orcas has been officially named as Visual Studio 2008, and can be oficailly downloaded as a BETA from here: Microsoft Download Site
This BETA is on a time trial until March 13, 2008 and available in English and Japanese.
Visual Studio 2008 will use and Updated version of C# (v3.0 and VB 9.0), as well as an updated .NET framework up to v3.5, however the CLR will remain the same as in Visual Studio 2005, CLR v2.0.
The IDE itself is no great leap from 2005, and is merely a superset of VS2005. Integration with the forthcoming Silverlight and better integration between numerours platforms.
Keep an Eye here for further updates, news and progress with Visual Studio 2008.