i don't think the forum software supports any voting restrictions. probably such a feature could be hacked in quite easily but i guess no one with access to the forum source will do this.

maybe someone could do a simple php voting script (without database requirement so that it can run anywhere) for the next contest. only the contestants get a password for voting. they can't vote for themselves but only for the other entries. everyone has 3 votes (first, second, third) since then it's less likely that entries get the same amount of points. i guess such a script could be done in an hour. just an idea...