another alternative is to use javascript to retrieve user information associated with the ip's machine then send that to a perl script where the information is manipulated. use the <img> tag in a web page to capture the information and send it to a perl script. You will probably want the perl script to return a 1x1 pixel blank image so it works properly.

<SCRIPT language=javascript>
//<!--var x;
x="";
x+="<img src='http://yoursite/cgi-bin/capture.cgi?page=";
x+=escape(location.pathname)+"&ref="+escape(document.referrer)+"&ua="+
+escape(navigator.userAgent)+"&plat=";
x+=escape(navigator.platform)+"&cooks="+escape(navigator.cookieEnabled
+)+"&cpu=";
x+=escape(navigator.cpuClass)+"&java="+escape(navigator.javaEnabled())
++"'>";
document.write(x);
//-->
</script>
[download]

this will capture several machine specific details that can be parsed by your perl program. Then in the capture.cgi you will want to simple use the ENV var to retrieve the ip address as you probably were.