Microsoft Libera el Primer Service Pack para el .NET FrameWork 3.5 y El Editor es su versión Beta. Realmente recomendaria NO instalarlo en máquinas de producción.
Incluye  la versión más reciente del ADO.NET Entity Framework and the ADO.NET Data Services framework (Astoria)
Lo puedes descargar en el siguiente Link :

.NET 3.5 SP1 and VS 2008 SP1 download center.

Copio de las notsa de release :

The new .NET Framework Client Profile Setup Package which provides a setup installer that enables a simpler installation for .NET client applications on machines that do not already have the .NET Framework installed. According to Microsoft’s Guthrie, the .NET Framework Client Profile setup contains just those assemblies and files in the .NET Framework that are typically used for client application scenarios;

*WPF data binding and editing improvements that include: StringFormat support within {{ Binding }} expressions to enable easy formatting of bound values and better handling and conversion support for null values in editable controls;

*Better Intellisense support within VS 2008 for popular Javascript libraries such as JQuery, Prototype, Scriptaculous, and ExtJS; and

.NET 3.5 SP1 and VS 2008 SP1 download center.