you can't use datatable like that...
use somthing like datarow to pick data and add it row by row in a temprory table then you may copy data from that datatable to anothor dataset.
DataTable dt = new DataTable("nicktable");
dt.Columns.Add("col1", Type.GetType("System.Int32"));
dt.Columns.Add("col2", Type.GetType("System.String"));
SqlDataAdapter adp = new SqlDataAdapter("select * from tbemp", ConfigurationManager.ConnectionStrings["cn"].ConnectionString);
DataSet ds = new DataSet();
adp.Fill(ds);
DataRow dr = dt.NewRow();
dr[0] = ds.Tables[0].Rows[0];
dt.ImportRow(dr);
DataSet dss = new DataSet();
dss.Tables.Add(dt);
hope this helps...