How to extract and save/read XML email attachment from stdin pipe?

Question

I have an email address piped to a php script which can catch the inbound data. The thing I need out of the email is the XML that is attached. I need to extract the XML attachment into a variable so I can parse it and do stuff with it.

I have the parsing routine down without an issue since I use it now fopen'ing data that I get using PEAR.

I don't know how to extract the XML file from the email data that is piped to the STDIN and assign it to a variable (or save it to disc if need be).

Any ideas gurus?