In both Visual Studio 2008 and 2010 there is a bug when you try to use the WCF Service Configuration Editor. The editor should be reachable through the Tools-menu or by right clicking a configuration file (web.config / app.config). This appears to be a known bug. It’s not blocking, but it’s easier to access the editor directly from the configuration file (then the file is immediately loaded in the editor). 

When you just started Visual Studio, and right-click a configuration file, the editor is not visible as an option:

Now open the editor from the tools menu (Tools –> WCF Service Configuration Editor):

Now the editor will open. You can close it immediately and go back to the configuration file. When you right-click it now, you will see that the option to open the editor is available: