For Houston to win I think JJ Watt has to play out of his mind and pressure Brady up the middle all day. It's been well documented the best way to effect Brady is to rush from the interior of the line and disrupt the pocket.
Getting Arian Foster and that running game going is crucial too, as Schaub has stunk for weeks (I don't know if he's injured or just choking but IMO the biggest difference during their collapse has been his play).
I think the biggest thing going for the Texans is the revenge/nobody believes in us factor.
That said, Pats are too good, too healthy. With the Broncos gone and the road to New Orleans going through Foxboro I have a hard time not seeing the Pats advancing to the Super Bowl.