LabVIEW's XML VIs only allow flattening and unflatting LabVIEW data to an XML string of the LabVIEW Data Schema type. There is not much support beyond that. I suggest that you use a real XML parser for doing what you are after. If you are using Windows, then you can use the Microsoft XML Parser which has an ActiveX interface which may be accessed from LabVIEW. Take a look at the LabXML Project on SourceForge.net. It includes some examples, which might be useful to you.
I am using the MS parser 3.0. However, if I want to get the attributes of a node, I basically have to treat them as child nodes. I would like to know if there is a get_attributes method (such as the one invokable from VB) associated with LV 6.1.