This handy tool from Yahoo Sports, the
Playoff Scenario Generator tells you how the playoff seedings will go based on the results of the season's final three weeks.
There are a number of default starting points to choose from (I chose each matchup won by best winning percentage) but you can then go back and tweak the outcome yourself. If you see the 49ers beating the Steelers in Week 15, just click that game and watch the playoff results change. If you think the Magic Tebows can upset the Patriots, change that too.
For Texan watchers, the most important thing is for the Steelers (whom we beat) to take the AFC North over the Ravens (who we lost to) in order for the Texans to get a first-round bye (assuming they win out over the Panthers, Colts and Titans). We can run the table but still wind up the #3 seed if the Ravens and Patriots also win out.