Starting with 2005, VS started this behavior of when starting debugging session it spawns up a webserver for every project in a solution. I have a solution with 15 projects
Set the web service project's "Always Start When Debugging" property to false. To get to the property, click on the project node and then hit F4 or click View | Properties Window (not Property Pages).
Be careful: this is not in the properties you reach by clicking the project node then clicking Properties; or by double-clicking the project's Properties sub-node; or by clicking View | Property Pages.
Also annoying is that this is property only persists as a user setting, in the .csproj.user file.