How to i write to a file in xml?

oDataSet = new DataSet();

XmlReadMode omode = oDataSet.ReadXml(PathSelection);

for (int i = 0; i < oDataSet.Tables[2].Rows.Count; i++)

{

string comment = oDataSet.Tables["data"].Rows[i][2].ToString();

string font = Between(comment, "[Font]","[/Font]");

string datestamp = Between(comment, "[DateStamp]", "[/DateStamp]");

string commentVal = Between(comment, "[Comment]", "[/Comment]");

string[] row = new string[] { oDataSet.Tables["data"].Rows[i][0].ToString(), oDataSet.Tables["data"].Rows[i][1].ToString(), font, datestamp, commentVal };

Gridview_Input.Rows.Add(row);

cboLanguage.Enabled = true;

btnNewfile.Enabled = true;

}