I would like to create a level editor for Silverlight with XAML. What resources would be useful for research before starting such a project?
Here is some information to clarify. I made 1 silverlight game and released it so far. The I would like to have an overhead style action game. The map would be much larger than the current viewable space.
Obviously getting to grips with XAML and how to work with it as a concept is important if you haven't already. An overview of it (using WPF as the example) can be found at MSDN here along with the System.Windows.Markup namespace which has the classes you would use for working with it.
WPF has a steep learning curve, don't get dis-heartened it's brilliant, but it has so many nooks and corners that it'll take a while to get comfortable. For a start there's a really good blogging community at WPFDisciples all of these are worth reading. Codeplex has some good libaries for 3D, physics engines etc and reverse engineering others code is a good way to learn.
A couple of good books are Windows Presentation Foundation Unleashed and Petzold's Applications = code + markup is one of the few books/places that doesn't preach that everything has to be done in Xaml
An area that takes some getting used to is binding, lots of stuff out there but it can be complex, and it's a impossible to debug until you have the magic knowledge. Binding in WPF isn't just about data, it's about linking all UI elements and behaviours together - it's really important.
Finally you have a choice between Silverlight and WPF, they're not the same. Although Silverlight is a good sub set of WPF, there are certain things you just can't do.
Finally Finally if you have a graphic design, artist background try using Blend, not VS it's a much better tool for those who are visually aware.