Bayan has published the schedule of the upcoming finals of their contest: http://en.bayancontest.ir/post/Contest-schedule
The contest should be quite compact: just two days and everything in the same hotel. All participants has to register themselves on Friday, February 15. Actually, the schedule does not say "February 15", it just says "Friday". Participants of the onsite event have got email invitations to Tehran for February 14-17, so let's assume we are talking about 15th of February, 2013. Speaking about dates, I have to mention that it's right now the year 1391 in Iranian Solar Hijri calendar. The New year is celebrated on March equinox, that's why the Sun is mentioned in the calendar name.
The contest will be held next day, on Saturday. All events should take place in the Parsian Azadi Hotel, which is located at the very north of the city next to Alborz mountains. Looks quite fascinating:
As far as I know, the Bayan Contest team has not communicated any transportation details to foreign participants. I checked out how you can get from the IKA airport to the hotel. One can take a bus to the subway station, cross the city in metro, exit near the Embassy of Russian Federation (Swiss Embassy is also nearby) and take a taxi. Here are the details: https://maps.google.com/maps/ms?msid=203576579397348428033.0004d54f4678ed65db970&msa=0 — please beware, this is not the official information, it's just my idea on getting around in Tehran.
UPD. All the participants will be welcomed and picked up at Imam Khomeini Airport by Bayan staffs, and will be transported to the hotel afterwards.