The only real tool for developing cross-platform rich Internet applications (RIAs) for that last 11 years has been Flash; until now! Silverlight 3 allows you to develop cross-platform rich Internet applications in a fraction of the time because of the extensive and very powerful .NET 3.5 libraries, the powerful, design friendly Blend 3 IDE, and an enhanced workflow that allows designers and developers to work on the same set of files at the same time.
Buy Foundation Expression Blend 3 with Silverlight by Victor Gaudioso from Australia's Online Independent Bookstore, BooksDirect.