You want Silverlight then you'll need the following:
The basic Silverlight 1.0 SDK - http://msdn.microsoft.com/vstudio/eula.aspx?id=a40f3ffc-2657-02ec-7d67-7a79b4eac832
And if you want to have access to managed code you'll need Silverlight 1.1 SDK - http://msdn.microsoft.com/vstudio/eula.aspx?id=c8bf88e7-841c-43fd-c63d-379943617f36
Supported Operating Systems: Apple Mac OS X; Windows 2000; Windows Server 2003; Windows Vista; Windows XP
There is a wide choice of devlopment environments including the Visual Studio Express editions and the new Expression Blend product.
Something else you might want is ZAM 3D from Electric Rain which is currently the best tool for creating 3D XAML resources.
Watch out for some specific tutorials and articles on Silverlight coming soon to Geekzilla.
Mark is trying not to drink too much 'cool aid' at the moment. All the more for everyone else!