This article has only scratched the surface of what XML is and what its possibilities are. For example I haven't addressed the information sharing options XML offers: it greatly eases the re-use of data across platforms. Below I have collected some resources with more information on XML.
MSDN and XML
About Excel and XML
About Word and XML
Professional Excel development
By Stephen Bullen, Rob Bovey and John Green
Published by Addison-Wesley, februari 2005.