I've just taken contact with the developer of the web service I'm trying to run. He answered me that the web service is correctly implemented. I tested it in a link he provided me...
I'm still thinking that something is lacking in my local EasyPHP installation...
I saw that the url I posted isn't the same one this forum shows. But this is not a problem, I tried other web services and no-one can run with my EasyPHP 5.3; I always get the same fatal error, either with a web service that I've implemented on my own. So I think that the same error will occurs with every web service I try.
The message says "cannot find the class SoapClient".
I'm still thinking that my php installation lacks of some extension, or some library. Is there a way to download and install such extensions?