XML Serialization

Question

Hi,
I want to do following two steps. I am already done with first step. But I can't do the second step. Could anyone give me any idea how to do it?
Step 1: After serialization, I load XML file's data in a datagrid in tabular format.
Step2 : Now I want to add row in datagrid. And I want to save newly added data  to same XML file.
Thanks
Neel