Is there a way to get the entire URL used to request the current page, including the anchor (the text after the # - I may be using the wrong word), in included pages?
i.e. page foo.php is included in bar.php. If I use your solution in foo.php, I need it to say bar.php?blarg=a#blahblahblah
You can't - you'll have to write the value of the hash to a cookie via Javascript to send it to the server on the subsequent request.
No, I am afraid not, since the hash (the bit after the #) never gets passed to the server, it is solely a behavioural property of the browser. The $_SERVER['REQUEST_URI'] variable will contain the rest however.
If you really need to know what the hash is, you will have to use the document.location.hash property, which contains the contents of the hash (you could then insert it in a form, or send it to the server with an ajax request).
You can pass up the full URL, including the anchor (the part after the #), using a Javascript onload function that sends that URL to an Ajax endpoint.