Convert Datatable To Byte Array To Send As Email Attachment

Every morning we send out an email with a text file attached. This is a manual process so I am automating it.I am using an internal mail web service. Its last two parameters are a byte array which is the file contents and a string which is the file name. I passed (...gbytes, "test.txt") and the only thing wrong with it is text.txt is XML. I want it to be text (csv is fine because there is actually four columns that come from a datatable).So I am assuming what's making it XML is this code:

Code:
System.IO.MemoryStream stream = new System.IO.MemoryStream();
System.Runtime.Serialization.IFormatter formatter = new System.Runtime.Serialization.Formatters.Binary.BinaryFormatter();
formatter.Serialize(stream, ds.Tables[0]);
gbytes = stream.GetBuffer();

I am trying to search the Internet for how to convert a datatable to a byte array, but I can't find how to have it be text instead of XML. Also, another parameter our WS takes is a flag to say if it's XML, and I am setting this to false.