Once you have the WSDL and have created (normally automatically via a tool) a client SOAP wrapper for that web service, calling a .NET web service versus calling any other web service (assuming the web service parameters and return types are "standard" interoperable types) should be the same.
The only layer you deal with is SOAP over HTTP. It doesn't care what the underlying language on the server or what kind of web server it is. It's just sending a special kind of HTTP message to a URL, and dealing with the HTTP response.