voting system

I want a voting system to work with my site (still under construction) that uses the joomla language. I am going to post an article of calculation in my blog against some authoritative theory. I am going to ask the public to submit arguments to refute my calculation. Any of such arguments will be posted in my blog in the category "against the webmaster" and receives votes from the public. If an argument receives 80% of the total votes, the owner of the argument will receive a $2,500 award from me. If no argument can receive 80% of the total votes, all those votes cast for the webmaster will equally share a total award of a huge sum, whose size will be determined later. Any voter can cast vote once only, either for me, the webmaster, or for the argument that is against my calculation. Fine tune: (1) How to prevent one person from casting multiple votes? (2) How to filter the education background of a voter, such as minimum freshman in college?