XPathReader is/ was an implementation of a forward reading XML parser (built on XMLReader) which allowed you to register XPath queries for it to find (or at least a subset o
I suspect that LINQ-to-XML happened. However, the Mvp.Xml project on CodePlex has many features that relate to this. You might want to take a look at the XPointer.NET library they have developed and the XPointerReader.
Also, you might want to take a look at this FastXPathReader on CodeProject (I don't know how effective it is).
As for XPathReader, all I could find were the links you provided and links associated with those. It looks like it disappeared. Like I said, I think LINQ-to-XML was the outcome, but I'm just guessing.