Gimme a 'Z.' ...Gimme another 'Z.' ...March Madness gets under way on Thursday, and by evening's end Kentucky will have successfully defended its national championship. In cheerleading, that is. The Wildcats, vying for their fourth straight title, take on nine other finalists in the 15th annual National Cheerleading Championships (ESPN, 9:30 p.m.), which were actually held in January in Orlando. If you don't give two bits about which cheerleading squad wins but do enjoy watching folks display a little school spirit, flip to the NCAA tournament.