First, use System.Net.WebClient to retrieve the content from
http://data.mtgox.com/api/2/BTCUSD/money/tickerThen, depending on how complex you wanna get, either just parse the result via Regex.Match to extract the "last" trade value, or alternatively the built-in DataContractJsonSerializer to map to a .NET class, or the built-in JsonReaderWriterFactory.CreateJsonReader will create XML from JSON, or find some free add-on libraries that will parse JSON (e.g.
http://json.codeplex.com/).