A quick look at what the 2010 NFL Rule Book says, verbatim, about overtime for postseason games:
Rule 16, Article 4
For postseason games, following a coin flip (Article 2 above) and an intermission of no more than three minutes after the end of the regular game, the following shall apply:
(a) Both teams must have the opportunity to possess the ball once during the extra period, unless the team that receives the opening kickoff (Team B) scores a touchdown on its initial possession, in which case it is the winner, or Team A scores a safety on Team B’s initial possession, in which case Team A is the winner.
(b) If the team that possesses the ball first scores a field goal on its initial possession, the other team (Team A) shall have the opportunity to possess the ball. If Team A scores a touchdown on its possession, it is the winner. If the score is tied after Team A’s possession, the team next scoring by any method shall be the winner.
(c) If the score is tied at the end of a 15-minute overtime period, or if Team B’s initial possession has not ended, another overtime period will begin, and play will continue, regardless of how many 15-minute periods are necessary.
(d) Between each overtime period, there shall be a two-minute intermission, but there shall be no halftime intermission after the second period. At the beginning of the third overtime period, the captain who lost the coin toss prior to the first overtime period shall have the first choice of the two privileges in Rule 4, Section 2, Article 2, unless the team that won the coin toss deferred.
(e) At the end of the first and third extra periods, etc., teams must change goals in accordance with Rule 4, Section 2, Article 3.
(f) A player is in possession when he is in firm grip and control of the ball inbounds (3-2-7). The defense gains possession when it catches, intercepts, or recovers a loose ball.
(g) The opportunity to possess applies only during kicking plays. A kickoff is the opportunity to possess for the receiving team. If the kicking team legally recovers the kick, the receiving team is considered to have had its opportunity. A punt or field goal that crosses the line of scrimmage and is muffed by the receiving team is considered to be an opportunity to possess for the receiving team. Normal touching rules by the kicking team apply.
(h) Each team is entitled to three timeouts during a half. If there is an excess timeout the usual rules shall apply (4-5).
(i) At the end of a second overtime period, timing rules shall apply as at the end of the first half. At the end of a fourth overtime period, timing rules shall apply as at the end of the fourth quarter.
(j) All replay reviews will be initiated by the replay assistant. Coaches’ challenges will not be allowed.