Aaron Brethorst, Program Manager for the Visual Studio - IDE team informed me about a new article on MSDN that explains the Visual Studio Support on Windows Vista.
The FAQ contains good answers to the common questions on why there is no Visual Studio.NET 2003 support and how to run Visual Studio 2005 with elevated privileges. There are several questions and workarounds worth reading.
I’m still considering wating for the non-beta version of the Visual Studio 2005 SP1 before migrating to Windows Vista.