HAVING already achieved massive stardom in nearly every corner of the world except the U.S., Puerto Rico native Ricky Martin now appears destined to become a household name in America as well. Thanks in large part to a show-stopping performance of his worldwide smash hit (and 1998 World Cup theme song), "La Copa de la Vida," at the Grammy Awards show in February 1999, Martin is being hailed as the frontrunner in a vanguard of Latin pop stars that includes Jennifer Lopez, Luis Miguel, Enrique Iglesias, and Chris Perez. Not only has his 1998 Spanish-language album, Vuelve, vaulted into the Billboard Top 100 (it still resides at No. 1 on the Billboard Latin 50 chart), but the debut single ("Livin' la Vida Loca") from Martin's first English-language album has become the biggest selling No. 1 single in the history of Columbia Records. And if that isn't enough, capping this onslaught of attention is a ringing endorsement from Madonna, who leapt at the chance to do a duet with Martin on his English-language debut.