Jack Nicholson's a three-time Oscar winner, but who knew he could sing? Stick around for the end credits of Something's Gotta Give and you can hear him croon the Edith Piaf classic ''La Vie En Rose.'' (On the soundtrack, Jack even tackles parts en francais.) ''One take,'' boasts the star. ''Gorgeous.'' So, how good is he? Quips jazzman Steve Tyrell, who produced the number, ''I'm going to get him to sing background on my next album -- if he needs any extra work.''