Call External Json Webservice From C#?

I need to make a call to a json webservice from C# Asp.net. The service returns a json object and the json data that the webservice wants look like this:

"data" : "my data"

This is what I've come up with but I can't understand how I add the data to my request and send it and then parse the json data that I get back.

string data = "test";
Uri address = new Uri("http://localhost/Service.svc/json");
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(address);
request.Method = "POST";
request.ContentType = "application/json; charset=utf-8";
string postData = "{"data":"" + data + ""}";

How can I add my json data to my request and then parse the response?