Currently the Class Designer allows you to edit the diagram (and thereby the code) through in-place editing of type and member names on the diagram. The Class Details Window lets you edit other properties of type members (fields, properties, methods and events) like access modifiers, types of members, parameters to methods etc.
If you don't have VS 2005, you can find a screenshot of the Class Details Window here (towards the end of the document). You can find how to create and modify Class Members here. The Class Details Window provides cool keyboard shortcuts (learn about it here).
I am interested in getting feedback on the Class Details Window.