If you need to get the Enterprise Library 3.1 Configuration Editor working in Visual Studio 2008, Scott Densmore from Microsoft Patterns & Practices uploaded a quick fix to the Enterprise Library Contribution CodePlex website that you can run to make a few registry changes.
Enterprise Library 4.0 will be available in its first CTP in a few days, Unity and Enterprise Library 4.0 Release Plans, and that should automatically install the Enterprise Library Configuration Editor in Visual Studio 2008. However, it will be a CTP as a part of Enterprise Library 4.0.
Scott Densmore has the details.