I'm only guessing, so those techies out there please don't shout at me for being stupid. I think it works by way of cookies. After you vote, you get a cookie placed on your computer, and you won't be able to vote again.
You can vote again by logging on to another user account, or even on the same account by simply removing the previous cookie.
Results may not be completely accurate, but one assumes people are being sensible about it.
Thanks. So can anyone personally recommend a site or where to go for the code that could provide me with a polling feature that automatically displays the results.
I know I could create this manually with forms and add up the email replies by hand but I don't know very much about php, cgi-bin scripts and I know nothing about planting cookies on other people's machine.