In IIS6, we had a separate node in the left pane to add/view/delete "Web Services Extensions". Here in IIS7 manager, it is presented as the "ISAPI and CGI Restrictions" and you can find this on the global level Features view:
Also, if you wonder where is the option to allow all Unknown ISAPI / CGI which was there earlier in IIS6, just right click and select "Edit Feature Settings..." or select the same from the "Actions" pane. Below are the screenshots:
Hope this helps! Happy Learning!