The .NET Framework 3.5 is required for Expression Blend 2 installation.

Use Expression Blend 2 to create and modify Windows Presentation Foundation applications that use the .NET Framework versions 3.0 or 3.5. You can also use Expression Blend 2 to create and modify Silverlight 1-based applications, including modifying Silverlight files that are generated by Expression Encoder 2. Expression Blend 2 creates Visual Studio 2008 project files, which cannot be opened in Visual Studio 2005. However, both Expression Blend 2 and Visual Studio 2005 can open projects that were created by using the first version of Expression Blend. Expression Blend 2 contains more features than Expression Blend with Service Pack 1, such as the ability to make a user control from a selection of objects on the artboard, to animation the vertices of a path, to use spline curves to change the easing behavior between keyframes, to embed fonts, and more.