The tools alpha refresh released today has the same feature-set as the Silverlight Tools Alpha add-on which was previously available for Visual Studio 2008 Beta2 (it has simply been updated to work with the final VS 2008 release). This feature-set includes basic Silverlight 1.1 project system support, XAML markup editing and intellisense support, debugging support, Expression Blend project compatibility, and VB and C# code-behind intellisense. You can find quickstart tutorials that detail how to use these features here.
The next public preview of Silverlight will include a ton of new runtime features, as well as a significantly enhanced VS 2008 tooling support. I'll be blogging more details about this shortly.
Hope this helps,