The problem is: if you "try different codes" instead of doing programming, even if you get some help, it would be useless for you. You did not explain how you work with XML in general, where the data should be inserted, what's your goal. The question has nothing to do with ASP.NET, so you should remove this tag.
So, here is some ideas: 1) XML is structured, so you can insert some data in XML node, not XML; 2) you should work with XML, not XML file; so, you can read and parse the whole XML, modify it, and write the whole thing to the file; you can do it if the data is small enough to fit in memory; 3) better yet, you should work with data, not with XML; so learn about
serialization and use it.
http://en.wikipedia.org/wiki/Serialization[
^],
http://msdn.microsoft.com/en-us/library/ms233843.aspx[
^],
http://msdn.microsoft.com/en-us/library/7ay27kt9%28v=vs.100%29.aspx[
^],
http://msdn.microsoft.com/en-us/library/ms733127.aspx[
^].
—SA