Not too sure about the byte array but you can loop through the DataSet a row
at a time and extract the column data a row at a time until there is no more
rows to process i.e something like -

MyApp.MyService.Service service  = new MyApp.MyService.Service();

DataSet ds = new DataSet();

ds = service.GetMyDataSet();

if(ds!= null)
{
  foreach(DataRow row in ds.Tables[0].Rows)
  {
     // fetch the data from the row columns i.e. row[0], row[1]
  }
}