[TYPO3] RealURL, URLTool, 404 page

[Lamb, Brian]

Hello all, 

I have RealURL and URLTool working correctly. This is probably not so
much a Typo3 question but it revolves around the RealURL works. I know
that whenever RealURL creates a page:
http://www.myserver.org/path/to/page, the path/to/page directory doesn't
actually exist on my server but it is Apache rewriting the url. 

Now, when a user visits a page that doesn't exist, I have a 404 page set
up to handle this. What I am looking to do is to grab the URL of the
broken page and then do something with it. 

Is this possible since the directory path doesn't exist? I try the usual
PHP server functions but cannot get the actual path. I thought
HTTP_REFERER would do it but it just returns an empty string. 

Thoughts?