ErrorDocument redirect with .htaccess

[lowtide]

I am using the ErrorDocument directive in an .htaccess file to redirect users to custom error pages (PHP script) on my site. In my PHP script I am able to capture the bad URL using $REQUEST_URI and make it the value of a hidden field in a form. The user can than submit the information if they beleive it was truly an error and not just a mistyping. What I would also like to do is capture the page where the URL was linked from so that I can troubleshoot the problem. Is there a way that I can do this? I have looked for a javascript solutions and could not find anything.

TIA

[sglane]

$HTTP_REFERER perhaps?

[damoe]

I already tried to use $HTTP_REFERER but it doesn't work for me. It seems that $HTTP_REFERER doesn't get any values.
Is this perhaps a problem of Apache configuration? Can anyone help me?