Good luck there. Petzold does have a WPF book. I don't think there are any widely acclaimed WPF bibles yet, though. WPF is still pretty new in the grand scheme. My team recently evaluated WPF and we didn't find that the books went deep enough to help us tackle what we wanted to accomplish. We just had to dig in ourselves and ask more experienced people on a case-by-case basis.
You may have already done this but, if I were trying to help a winforms programmer pick up WPF, here is what I would have them do:
1. Read the Josh Smith MVVM article and accept MVVM as your new way of life.
2. Watch the Jason Dolinger video (http://blog.lab49.com/archives/2650
3. Keep things simple and straightforward, even if it seems tedious. I'd stick to INotifyPropertyChanged and avoid DependencyProperty, for instance.
4. Start writing some toy apps until you know what's going on. Apps like a kitchen timer simulator or Windows Calculator or Notepad.
Programming with WPF can be drag-and-drop if you want it to be. Else, it's a lot like writing GUIs in a desktop dialect of HTML, then mating them up to your program's objects with XPath.
That video is pretty illustrative.