I have seen lots of questions recently about WPF...
WPF is the next frontier with Windows UIs.
You can get either Adam Nathan's WPF Unleashed Book or Chris Sells Programming WPF .. those seem to be the way to go. I just read the first chapter of Adam's (Lead for WPF at MS) book. Hence the WPF praise fountains :)
WPF is part of the .net 3.0 stack. Its microsoft's next generation Graphical User Interface system. All the information you need can be found on wikipedia and msdn's wpf site
To Get Started programming I guess check out the essential downloads on windows client
Take a look here http://windowsclient.net/ and here Windows Presentation Foundation (WPF)
Basically WPF is created to make windows form easier to design because of the use of XAML, designers can work on the design and programmers on the underlying code
Windows Presentation Foundation. It's basically Microsoft's latest attempt to make development easier, and provide a whole heap of nice functionality out of the box. I'm not sure where to start, but googling "WPF 101" should throw up a few useful links.
WPF is the Windows Presentation Foundation. It is Microsoft's newest API for building applications with User Interfaces (UIs), working for both standalone and web-based applications.
Unsurprisingly, there is a very detailed but not all that helpful Windows Presentation Foundation page at Wikipedia.
The WPF Getting Started Page at the Microsoft MSDN site is probably a better place to start.
Check out Eric Sink's Twelve days of WPF 3D.