Collecting user informtion.

[Guest daleosmond]

hey,
im developing an secure login system.
im using sessions and just case someones "steals" another users session id i want to add a certin part
of imformation in to the sesson and php will compair the ips to make user they are correct.
ONE problem bloody AOL is know to dramaticly change ips while surfing.

so does anyone know an piece of information that i could collect from an user?
$_SERVER['somethink']; maybe ?!? [img src=\"style_emoticons/[#EMO_DIR#]/smile.gif\" style=\"vertical-align:middle\" emoid=\":smile:\" border=\"0\" alt=\"smile.gif\" /]