From what I hear, it comes down to this:
The Big Ten will have two BCS teams. If Oklahoma State beats Oklahoma, Okie State goes to the Fiesta Bowl as the replacement for Texas, and the Orange Bowl will take Penn State. If Oklahoma wins, the Big 12 only gets one BCS team (barring Nebraska upsetting Texas in the B12 title game) and the Fiesta Bowl will take Iowa. Either way, this puts us in the Insight Bowl, because we all know the Alamo wants no part of Minnesota.
If Oklahoma wins and finishes 7-5, they would probably move ahead of 8-4 Missouri in the pecking order: Okie State to the Cotton, Nebraska to the Holiday, Texas Tech to the Alamo, Oklahoma to the Sun, Missouri to the Insight, Texas A&M to the Texas, Iowa State to the Independence.
In the event of an Okie State win, that bumps everyone up a notch in the Big 12 pecking order. Nebraska to the Cotton, Texas Tech to the Holiday, Missouri to the Alamo. Then there's a glut of 6-6 teams: Oklahoma, Texas A&M, Iowa State. Oklahoma, obviously, would be the most attractive and would go to the Sun, leaving the Insight to choose between A&M and ISU. A&M is more desirable, but they would likely rather play closer to home in the Texas Bowl, and it's not like ISU would travel poorly to Tempe, so I believe a deal would be arranged for the Insight to snag Iowa State.