You could set the dataentry property to true for your new user form. That will hide all existing data.
There are a couple ways to go about preventing duplicates. One is to store the vote in the voters table directly. If you only have one vote per user, this makes sense. If you want users to vote on a variety of topics, but only once per topic, then votes should be stored in a seperate table. In this scenario, you do have to intervene to make sure there are no duplicates. One method is to simply disable the command button after it's been pressed. A more reliable method is to do some checking in the before_update event of the form to see if the vote already exists.