DataContractSerializer – how can I output the xml to a string (as opposed to a file)

Something like this – put your output into a MemoryStream and then read that back in:

public static string DataContractSerializeObject<T>(T objectToSerialize)
{
    using(MemoryStream memStm = new MemoryStream())
    {
        var serializer = new DataContractSerializer(typeof(T));
        serializer.WriteObject(memStm, objectToSerialize);

        memStm.Seek(0, SeekOrigin.Begin);

        using(var streamReader = new StreamReader(memStm))
        {
             string result = streamReader.ReadToEnd();
             return result;
        }
    }
}