Short answers, pulled from the story.
Hurricane Katrina struck New Orleans on the 29th of August 2005, and the flooding surrounding the New Orleans Arena made it impossible to use, even though the building itself sustained only slight damage. The Hornets relocated to Oklahoma City for the 2005-06 and 2006-07 seasons before returning permanently for the 2007-08 season.
The Hornets played the majority of their home games at the Ford Center in Oklahoma City, with additional games at the Pete Maravich Assembly Center in Baton Rouge and the Lloyd Noble Center in Norman, Oklahoma. They also played some games at the New Orleans Arena once repairs were completed.
The Hornets made their permanent return on the 31st of October 2007, defeating the Sacramento Kings 109-90 to open the 2007-08 season. The NBA had announced on the 31st of January 2006, that the team would stay in Oklahoma City for the 2006-07 season before returning home.
Oklahoma City fans gave the Hornets strong support, with the team averaging 18,168 fans per game at the Ford Center, a 78% increase over their attendance from the previous season in New Orleans. Mayor Mick Cornett said the city had exceeded even his lofty expectations.
Following the success of the Hornets' two-year tenure in Oklahoma City, the Seattle SuperSonics relocated there for the 2008-09 season and became the Oklahoma City Thunder. The Hornets' stay demonstrated that Oklahoma City could sustain an NBA franchise.
The New Orleans/Oklahoma City Hornets played the first professional sports event in New Orleans after Hurricane Katrina on the 8th of March 2006, losing to the Los Angeles Lakers.