should i need to install xml library in postgresql inorder to work on xml file?

Hello,

            I
installed postgresql on my sytem,I need to parse an xml file.When I am
working on xpath() it is showing an error that function is notfound and
i tried almost all xml functions in postgresql but it is giving me the
same result.why so ? should I have to install any xml library inorder
to avoid this?Please tell me its very important for me.

Thanks,

Avin.