เขียน winapp เรียก web service ปตท. จะเอาข้อมูลมาใช้ยังไงครับ

string xmlData = "<PTT_DS>\n <DataAccess>\n <PRICE_DATE>2013-02-16T05:00:00+07:00</PRICE_DATE>\n
<PRODUCT>Blue Gasoline 95</PRODUCT>\n <PRICE>48.95</PRICE>\n </DataAccess>\n <DataAccess>\n <PRICE_DATE>2013-02-16T05:00:00+07:00</PRICE_DATE>\n
<PRODUCT>Blue Gasoline 91</PRODUCT>\n <PRICE>46.45</PRICE>\n </DataAccess>\n <DataAccess>\n <PRICE_DATE>2013-02-07T05:00:00+07:00</PRICE_DATE>\n
<PRODUCT>Blue Diesel</PRODUCT>\n <PRICE>29.99</PRICE>\n </DataAccess>\n <DataAccess>\n <PRICE_DATE>2013-02-16T05:00:00+07:00</PRICE_DATE>\n <PRODUCT>Blue Gasohol 91</PRODUCT>\n <PRICE>38.08</PRICE>\n </DataAccess>\n <DataAccess>\n <PRICE_DATE>2013-02-16T05:00:00+07:00</PRICE_DATE>\n <PRODUCT>Blue Gasohol E20</PRODUCT>\n <PRICE>35.08</PRICE>\n </DataAccess>\n <DataAccess>\n <PRICE_DATE>2012-04-16T00:01:00+07:00</PRICE_DATE>\n <PRODUCT>เอ็นจีวี</PRODUCT>\n <PRICE>10.5</PRICE>\n </DataAccess>\n <DataAccess>\n <PRICE_DATE>2013-02-16T05:00:00+07:00</PRICE_DATE>\n <PRODUCT>Blue Gasohol 95</PRODUCT>\n <PRICE>40.53</PRICE>\n </DataAccess>\n <DataAccess>\n <PRICE_DATE>2009-10-01T05:00:00+07:00</PRICE_DATE>\n <PRODUCT>ดีเซลปาล์ม</PRODUCT>\n </DataAccess>\n <DataAccess>\n <PRICE_DATE>2011-03-01T06:00:00+07:00</PRICE_DATE>\n <PRODUCT>Blue Diesel B5</PRODUCT>\n </DataAccess>\n <DataAccess>\n <PRICE_DATE>2013-02-16T05:00:00+07:00</PRICE_DATE>\n <PRODUCT>Blue Gasohol E85</PRODUCT>\n <PRICE>23.38</PRICE>\n </DataAccess>\n</PTT_DS>";

StringReader reader = new StringReader(xmlData);
DataSet ds= new DataSet();
ds.ReadXml(reader);