By ROBERT PHILPOT Michael Johnson is perhaps best known as a four-time Olympic gold-medal winner, and for the 1996 Summer Olympics, in which he was the first man to win gold in both the 200- and 400-meter races. But he's also a businessman, with a background that goes all the way back to his days at Baylor University.He has been a motivational speaker, founded a sports-management company and, in 2007, opened the Michael Johnson Performance Center, a training center for amateur and pro athletes in McKinney.Small wonder that the Dallas-area resident was picked for this season of The Celebrity Apprentice, where he's one of the steadier presences in a series that features a motley crew of celebs that includes singer Cyndi Lauper, Poison lead singer Bret Michaels (both of whom reveal some surprising sides to their personalities) and former Illinois Gov.