Poll script?

Hello all,
I will have a meeting with a customer who wants a poll script. I know there are lots of free ones, I can either show him some free ones and get some consulting fee or just do custom one for him.
But my question is different;
I know that I can use cookie or IP number to keep track of who has voted. Are there any other way? Because they can disable cookies, or they may connect from proxy so all people coming from proxy will have same IP if I am not wrong.
Any better way?
Thanks

You could write one in PHP and use a session_id to store the details.

http://www.php.net and http://www.phpbuilder.com are 2 sites that might help :)

rgds,

Hello Keith
Thanks for answer. I checked php.net about session(there is huge discussion going on there about sessions) and I saw that sessions are in a way using cookies. If cookies are disabled, session are disabled( with php.ini you can set so if cookie disabled session id is added to URL). I am not sure If I am allowed on client machine to change php.ini file.
What I am thinking is that keep IP numbers for few hours in a table, and do not let them vote in that time range(I dont think this is good idea but idea). Or in a poll form put a unique hidden id from the database table and IP into table. And from that combination just let them vote once(It only prevents them go back and vote again).
I have never thought poll could be this complex:)
rgrds(Thanks keithMcL for answer again)