export excel to xml

This article shows how to read an Excel file and write to a database. You can use the same article to read an Excel file.

Import data from Excel to Access using ADO.net by Vandita Pandey on Mar 04, 2007
Data interoperability with Microsoft office applications has become easier with ADO.net.

After that, you can use XmlWriter and related classes to write to XML. Here is an ebook on how to write Xml files.

Programming XML with C# is a 65 pages book written for C# programmers who wish to learn how to work with XML documents using C# language.