Resizing of the childwindows is not supported in silverlight 3 beta which might be possible in the RTM version, but until then here is one way we can style it and get the resizing to work
I took the style of the ChildWindow and added a Canvas in the style and added 4 thumbs one on each side of the window. Their size is .5px. so they dont change the look of the childwindow. when you mouse over near the borders you can see the visual cue from the cursors, The dragDelta event is handled to resize the window.
we can follow the same logic to get the resize behavior to work with Floatable window