Sure, there were millions watching football at this year's Super Bowl - but it was the Dixie Chicks' stirring national anthem and Shania Twain's eye-popping, explosive half-time show that grabbed the spotlight.  Two of country's main men also made appearances - in the game's much-hyped commercials.  Tim McGraw was seen behind the wheel as designated driver in an ad for Anheuser-Busch, while an IRS-wary Willie Nelson pitched shaving cream to pay taxes in a hilarious H&R Block spot.  Then, of course, there was the game.