It is my understanding that polls are only enabled under the "Polls" forum at this time. Jeff posted in a sticky message in that forum that they had accidentally been disabled for some time (I think since the new site implementation) but that they are enabled now. His message will explain how to do it, but once you try it in that forum, it is probably self-explanatory. If you need help beyond that, let me know and I'll guide you through it.
I think it would be nice if the polls forum was moved to the main Tickling Discussion forum and polls were just enabled for most forums, as most people don't look in Polls and many questions in the other forums would be better served with the addition of a poll. Hopefully this happens, but for now, I think it's just restricted to that one forum.