Read custom configuration file in C# (Framework 4.0)

 // Map the roaming configuration file. This
      // enables the application to access 
      // the configuration file using the
      // System.Configuration.Configuration class
      ExeConfigurationFileMap configFileMap =
        new ExeConfigurationFileMap();
      configFileMap.ExeConfigFilename = 
        roamingConfig.FilePath;

      // Get the mapped configuration file.
      Configuration config =
        ConfigurationManager.OpenMappedExeConfiguration(
          configFileMap, ConfigurationUserLevel.None);

from http://msdn.microsoft.com/en-us/library/system.configuration.configurationmanager.aspx