manage drop down box

I'm not a expierienced in script language, and what i want do requiers knowledge about script language. i want to make a form for my site where user can select a team from a drop-down box (eg i want to put 20 team or more) and after submit, the chosen team to be automatically deleted(disappear) from the drop-down box and can no longer be select by another user . The next user will see only 19 team, and so for the next and next....