Convert JSON formated String to JsonObject with Jayrock
Assuming json is the variable containing JSON text, use Jayrock.Json.Conversion.JsonConvert.Import(json). What you will get back in return is either a JsonObject, JsonArray, JsonNumber, System.String, System.Boolean or a null reference depending on the root JSON value in the source JSON text. If you know it is going to be a JSON object for sure then you can safely cast the return value or use JsonConvert.Import<JsonObject>(json).
I would discourage working against JsonObject directly unless you particularly depend on one of its features. You should just pretend the JSON object you get back is a dictionary; either IDictionary or IDictionary<string, object>. With the latest version for .NET Framework 4, you can also work with a JsonObject as a dynamic object.
I don't know Jayrock, but if you want to accept a JSON object as a parameter of Action in MVC2 than the easiest way to do it is by using JsonValueProviderFactory from Futures assembly.
It's part of System.Web.Mvc in MVC3.