I tried using OpenOffice but it does not support XML mapping. It may be added at some time but the last current version that I tried did not support XML mapping. The OpenOffice forum made no mention of XML mapping that I could find. You might want to start a OO forum topic of XML mapping and see what happens.
I wanted to use OO because it was free and cross platform capable, but no joy.
Update 03/24/2011: I believe that the all future posts concerning an XML file viewer application have been relocated to viewtopic.php?f=10&t=1872