t's one of the best kept secrets in Tinseltown. Totally on the QT, totally on the hush-hush, and it's got Tom Cruise's name all over it. It could also be this summer's biggest blockbuster. At least that's what everyone in Hollywood is saying about his newest movie, Mission: Impossible 2.    Like Stanley Kubrick's Eyes Wide Shut, lips are sealed shut about his return as Ethan Hunt, stealth operative of the fictional IMF agency. The follow up to 1996's Mission: Impossible, a take-off of the popular 1960s television show, M:I-2 has Hunt combating the threat of global biological warfare under the guidance of director John Woo.    Hunt takes on the mission to travel the world in search of an agent-turned-villain who knows the secret location of a deadly synthetic virus. He also discovers that his lead was a former lover of his teammate and bedmate Nyah Nordoff-Hall, played by Thandie Newton. Along with M:I alumnus Ving Rhames and legendary actor Anthony Hopkins, she goes undercover to seduce the unsuspecting terrorist and locate the virus. But things don't go as planned.    Like the plot of M:I-2, Cruise's life seems just as unplanned. Born Thomas Cruise Mapother IV, he was the third of four children to his father Thomas, an electrical engineer and Mary, a special-education teacher. As a child, he had to grapple with the hardships of divorced parents, constant relocation and dyslexia. While he always wanted to be on the field playing sports, no one thought this small time kid would turn into one of the biggest celebrity vehicles in the world.    It started in 1981 when Cruise was cast in Taps as a psycho-killer cadet. Two years later, at only 21 years-old, he had his big break in Risky Business when he slid on his Ray-Bans, tube socks and tightie-whities and lip-synched to Bob Seger's "Old Time Rock & Roll". With all eyes on Cruise, the rest of the eighties treated him with a series of box-office hits like Top Gun, The Color of Money and Cocktail.    In 1988, he threw in the macho towel for his performance in the Academy Award winning movie Rain Man. The film gave Cruise the credibility to play a serious lead role and earned an Oscar for Dustin Hoffman. Cruise thought it would be his turn to grab the golden statuette for his portrayal of Vietnam war vet Ron