I just posted this in response to a question about XPaths and Javascript on Stackoverflow:
I would look for an XSLT javascript library. Since most modern browsers have built-in XSLT support, and XSLT includes support for XPath, it is possible to use that engine to power your XPath selectors.Personally, I've used Sarissa and the Glyphix jQuery.xslTransform libraries successfully:
This looks interesting too: