Darryl Taft has an article on eWeek that outlines Why Vista Matters to Developers. As Jim Allchin notes, you can build applications that take advantage of the new technologies in Windows Vista today using Visual Studio 2005 (see Ready for a New Day for extensions to Visual Studio 2005 that provide some of the advancements you'll find in Visual Studio code name "Orcas").
Developers can use the existing Microsoft tool set, Visual Studio 2005, to build applications for Vista, Allchin said. The next major revision of the tools platform, code-named Orcas, will improve development for Vista, but "you can use what's available today," Allchin said.
Source: Why Vista Matters to Developers