Finding a refering domain

[Anon]

I'm building a traffic trading script similar to various Circle Jerk Scripts, but instead of using perl and flat-files I'm using PHP and MySQL.

To track hits I want to find the domain name i.e. joeblow.com or hellokiddies.net. I've tried using
$sender=$SERVER_NAME;
But that seems to give my server name...

Any suggestions?

[baruch]

You need the HTTP_REFERER variable, it holds the url from which the user arrived. That is, assuming he doesn't use a proxy that strips it.