Click in the forum you want to start it in. Click on "thread title" box like you did to start this. Then on the right is a "more options" box. Click that and it will take you to the full options setup.
Down at the bottom of the screen is the option to post a poll.
Oh and for the benefit of everyone always "Allow the results to be viewed without voting " That lets people see the results without having to vote, when you force people to vote to see it you get bad input in the poll in my opinion.