I try to use this function to prevent that the same visitor vote for more than one time in a hour but it don't work, the code is this:
if($vote!=1)
{
$time=time();
$time=$time + 36000;
setcookie("vote","1",$time);
}

If the visitor vote, the vote counts, than if he try to vote again the vote don't count, but if he try again it counts, the cookie is delete and i don't know why, i use IE 5.5. 
Can some one help me.