This version is an update to MVVM Helpers that is built on Visual Studio 2010 RTM. It includes some minor updates to classes and a few new converters and behaviors, but overall was specifically just a rebuild for .NET 4 release. The project template included in this release is for Visual Studio 2010.
This also includes a version for Silverlight - download the Silverlight package. It is a subset of the WPF version and I'm working on it as SL4 continues.