Johnny, I assume the top-tanks voting is PHP, if so, all you need to do is add some way to prevent the same IP from voting over and over. All of the tanks have unique ID's so just add a list of the IP's that have voted for that tank in the tank's data file. It would be really easy to collect:
Code:
<input type="hidden" name="voter_IP" value="<? echo($REMOTE_ADDR) ?>">
HTH,
Josh