string _userName = "", _password = "";
string _developerKey = "mydevelopperkey";
YouTubeRequestSettings _settings;


void GetListOfSubs(string username, string password)
{
      _settings = new YouTubeRequestSettings("My Subscribers", _developerKey, username, password);
      YouTubeRequest request = new YouTubeRequest(_settings);
      listBox1.Items = /*Subscribers from username*/
      //Here is my problem. How to get the subscribers?
}