I've created a sample project that demonstrates 2 ways to place custom buttons next to the navigation ones.
The first one shows how you can place an overlayed panel that still works when the window is resized.
The second one features modifications on our default scrollbar styles, but I would not recommend this approach because it is quite cumbersome and incorrect from architectural point of view.
There is also a third example that demonstrates how to ignore the default navigation buttons and create your own.
As for the Drag And Drop Framework - we will be releasing it only for Silverlight with the forthcoming Q3 release. We will plan porting the framework to WPF for Q1 2009. However, considering the complexity of the feature, we cannot set a certain timeframe at the moment.
Hope this works for you.
All the best,
the Telerik team
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