I’ve had a number of people ask me about intellisense with Silverlight 1.0 on VS 2008.  The trick is to *not* use the WPF Editor (the one that won’t show Silverlight WPF anyway).  To make it work:

• Right click the XAML file in the solution and pick “Open With…”.
• Pick “XML Editor”
• Click “Set as Default” if you want it to always open XAML files in the XML Editor…

Voila…