Microsoft Expression Blend is used to create the rich graphical interfaces that are the proverbial bread and butter of Windows Presentation Foundation and Silverlight applications.
Blend targets application designers as opposed to developers, but, as Microsoft sees it, designers and developers will increasingly be cooperating in the application development lifecycle. Blend’s hook is that the UI elements made by designers come with a code-behind XAML file, which can then be easily read by Visual Studio.
Microsoft’s Expression Blend Service Pack 1 takes a logical step and makes the tool compatible with the recently released Visual Studio 2008. Additional features of the download are covered in the Knowledge Base articles Description of Expression Blend Service Pack 1 and Issues that are fixed in Expression Blend by Expression Blend Service Pack 1.