using System.Net.Json;

public string ConvertHashtableToJson(Hashtable data)
{
    JsonObjectCollection result = new JsonObjectCollection();

    foreach(DictionaryEntry item in data)
    {
        result.Add(new JsonStringValue(item.Key.ToString(),
            item.Value.ToString()));
    } 

    return result.ToString();
}

public Hashtable ConvertJsonToHashtable(string json)
{
    JsonTextParser parse = new JsonTextParser();
    JsonObject object = parse.Parse(json);
    Hashtable result = new Hashtable();

    foreach(JsonObject item in obj as JsonObjectCollection)
    {
        result.add(item.Name, item.GetValue().ToString());
    }
}