Stopping Dual Ids on a public forum

Hi,

I am not sure whether this topic has already been posted or not here before but I am looking for a method by which I will be able to stop someone using multiple ids on a public forum. Is it possible or not. E-g cponsider this AO website how can one stop the person from using double ids as it will be unfair for polls and stuff like that.

I have almost done coding the forum and it will be up soon. This is one feature which I want in it to be present in my site.

Thanks in advance. I really appreciate it.

Regards.

Well, I guess it is possible to make some sort of hash out of the users IP and Browser or something like that and check if the hash is the same on later accounts, you can also check for multiple emails (same) and other info that is the same. If they were on a LAN/Cable/DSL you could just request their MAC addresses and check to see if that MAC is trying to register again. There is probably a much simpler way to do this. I just don't know it. :)

Well, I guess that hashing will not be of any use for dial up connections.