How to obtain clients IP adress

If your app runs proxied under Apache use this:
request.env[ 'HTTP_X_FORWARDED_FOR' ]

Direct requests:
request.env[ 'REMOTE_ADDR' ]

You realize most your AOL (and other large ISPs) visitors will appear
to be coming from the same IP addresses right?

You might go ahead and store the IPs but then also take into account
the time span since the last rating was recorded. If it's less than
24 hours ignore it or whatever.

That's sorta what I do in my free image rating script:
http://destiney.com/php#Destiney_rated_images