WPF Toolkit is a collection of new features and controls added to WPF. Some of the controls added to the toolkit are WPF DataGrid, DatePicker and Calendar Control, Visual State Manager, and Ribben.
You must have Visual Studio 2008 SP1 and .NET Framework 3.5 SP1 before you install WPF Toolkit.
Download and read more about WPT Toolkit here:
http://wpf.codeplex.com/Release/ProjectReleases.aspx?ReleaseId=22567