Winform and XML

Question

Hi,

I have a simple xml as below :
<NewDataSet>
  <Table1>
  <Product>1</Product>
  <Cost>134</Cost>
  </Table1>
  <Table1>
  <Product>2</Product>
  <Cost>224</Cost>
  </Table1>
</NewDataSet>

I am designing a datagridview, with 3 text boxes.

1) In the first col user must only choose the product value (1,2,3,etc) otherwise throw error
2) In the second col user can enter only numbers (quantity)
3) In the third col, I want the cost x quantity auto-calculated

Any help with code/url for these 3 questions above will be useful

Please help. Thanks !