Hi again !
I couldn't resist doing some research myself :-)
The IIS7 interface is quite different, but I think I've figured out a way to do this, which may og may not be the best way to go !
The process is very similar to the IIS6 process but things are called different names and the interface is quite different. The one we are looking for is called "Handler mappings" in IIS7, and then you have 3 options of adding handlers (Managed handler, Script map and Module mapping). I added a Script Map for the *.wgx file extsions, with the same executable as for the .aspx, the rest of things being the same as adding in IIS6 (unchecking the require file to be present etc.).
Adding the VWG Catalog application to IIS7 was a piece of cake after that, except for the fact that it didn't work :-) Just errors about the config:
Description: This application is running in an application pool that uses the Integrated .NET mode. This is the preferred mode for running ASP.NET applications on the current and future version of IIS.
In this mode, the application should not specify ASP.NET handler mappings in the <system.web>/<httpHandlers> configuration section. Instead, it should use the <system.webServer>/<handlers> configuration section to configure ASP.NET handler mappings. You have the following options:
Anyway, moving the app to the "Classic .NET application pool", via Advanced settins on the app seem to have solved that one.
And, now VWG Catalog app running on my Vista IIS7!