Modifying XML file

Hello there,

    Let's say I have 2 XML nodes <a>, and <c>.  My
ultimate goal is to add a third node, <b>, in between
<a>, and <c> in the XML file.  I would like to do this
using an XSL transformation, with both the original
file and the output file in XML format.  What would
this part of the XSL look like?  Also, for the output
to be in XML format, do I ONLY need to change the
output method to "xml", or is there more to it? 
Thanks so much.

Jonathan

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