如何在visual studio 2008中添加服务引用，以对受密码保护的Web服务进行身份验证

I want to reference a web service, and it requires user/pass authentication. In VS 2008, if I try to "add reference", or "add service reference", all I can type is the URL, there's no way to input my credentials. Obviously, if I try to load the ws, it shows me a nice message: I want to reference a web service, and it requi