I created the beginnings of a WPF Virtual Earth control. That's right, one you can just reference, add to your XAML, and start programming against without having to know the dirty underbelly of how it is implemented.
I decided to use the new WPF WebBrowser control that is in the .NET Framework 3.5 SP1. The WPF WebBrowser control is similar to the WinForms WebBrowser. The WPF WebBrowser control has the same z-order as it's WinForms counterpart, but it eliminates the need for WinForms interop.
The WPF map control allows you to create WPF UserControls and have them appear on top of the map:
In the picture above, the InfoBox, which is the term Virtual Earth uses for the UI that pops up when you hover over a pushpin, is a UserControl that uses WPF databinding to show Title and Description. I am clearly not taking advantage of the power of WPF in this example, but you get the point:). You achieve this through the following code:
You set the InfoBox property of the map to an instance of your UserControl. The map control does all the heavy lifting of positioning/showing/hiding your UserControl. The map control also allows you to add as many UserControls as you'd like through map.AddControl. However, you are responsible for positioning the controls yourself. In the picture below, I have replaced the default Virtual Earth Dashboard control with a UserControl containing WPF buttons:
If the WPF WebBrowser control still has the z-order issue, then how am I rendering WPF content on top of the map? I am using what I have been calling "layered window trickery" for lack of a better term. The map control loads a transparent window with a higher z-order than the window the control is in. The map control places the transparent window itself "covering" the area of the map control. Since the top window is transparent, interaction with the map below behaves as if there isn't a window over the map control. When a call is made to map.AddControl() or to set the map.InfoBox property, I actually add the UserControl to the top window. As you can imagine there is a bit of repositioning logic for the top window & WPF UI over top of the map. I plan on recording a Channel 9 Screencast walking through the code. If you can't wait, then you can just download the sample here and dig through it yourself. The control uses new features in the .NET Framework 3.5 SP1. Make sure you install Visual Studio 2008 SP1 Beta before trying to open it. Details here.