First of all the myth about the school buses is a lie. They didn't have 2,000. Media Matter has the facts on this out now.
http://mediamatters.org/items/200509120005
On September 11, ABC host George Stephanopoulos repeated a falsehood that had reverberated through the right-wing media the preceding week -- that "there were 2,000 buses under water" that New Orleans Mayor C. Ray Nagin could have used to evacuate his city before Hurricane Katrina's arrival. The claim appears to have originated in a September 6 column by Washington Times editor-in-chief Wesley Pruden, who inaccurately charged that, although Nagin ordered a mandatory evacuation before the hurricane's arrival, he "kept the city's 2,000 school buses parked and locked in neat rows when there was still time to take the refugees to higher ground." Conservative websites, including the Power Line and Little Green Footballs weblogs, quickly linked to Pruden's column.
This is a lie. Here are the facts.
Apparently, those school buses constituted the majority of New Orleans' school bus fleet. According to a September 5, 2003, article in the New Orleans Times-Picayune, "The [Orleans Parish school] district owns 324 buses but 70 are broken down." A 2003 document posted on the Louisiana Department of Education's website confirms that Orleans Parish used 324 "board owned" school buses and no "contractor owned" school buses.
More here
But Gingrich's claim has no basis in fact. While estimates of the number of residents stranded in New Orleans following the storm vary, New Orleans officials have suggested that 80 percent of the city's residents evacuated before the hurricane hit. That leaves roughly 97,000 residents who remained in New Orleans.
New Orleans' combined fleet of public transit and school buses would not have had nearly enough capacity to evacuate all of those who remained in the city. A July 8 Times-Picayune article, titled "RTA buses would be used for evacuation; But plan still falls far short of needs," pointed out that the RTA owned 364 public buses. "Even if the entire fleet was used," the Times-Picayune noted, "the buses would carry only about 22,000 people out of the city -- far short of the 134,000 people estimated to be without cars in a recent University of New Orleans study." Even the addition of the full school bus fleet would have been far from sufficient to transport the remaining residents.
These are the facts from Media Matters. Since this is Katrina related I'll watch out for comments if this has been daired already I'll delete.