i wouldnt use drop down lists - if you use option boxes, and then name the first ones "1st", second "2nd" etc, then it will only let you select one from each. That way you could list all the items each with 6 option boxes next to them, and they'd only be able to select a position once. Dont know if that messes around with your layout, but it's how i'd do it.
Also how much help do you need setting up the database? if you really have no idea, then i'd check the MySQL manual (http://www.mysql.com), or possibly invest in a good book (I use Web development using PHP and MySQL by Luke welling and laura thompson).