The WPF samples (along with all the other WinFX samples) in the windows SDK are installed as a zipped up file called "allwinfxsamples.zip" that is located at "C:\Program Files\Microsoft SDKs\Windows\v1.0\samples" (assuming you installed the SDK to its default location). There are lots of useful samples organized by topic, with sample code in VB.NET/C# and XAML.
If you need to find out how to do something with the latest release these samples are often your best source of information because they should all work against that version of WPF you have installed. Unfortunately because WPF is still being refined samples published on the internet can quickly become broken as new versions of WPF are released. Although in many cases the changes required to "forward port" samples to the new version are not difficult the SDK samples have a distinct advantage here because they target a specific release.