There is no mention of Bill Gates owning even a small portion of Apple in either his About.com or Wikipedia entries. This means that, unless this is a topic that has not been brought to the public, Bill Gates does not own any part of Apple.
According to Wikipedia, Bill Gates and Steve Jobs did meet at the All Things Digital conference in 2007. Also, a film named "Pirates of the Silicon Valley" was released in 1999 detailing the inception of both Apple and Microsoft during the final three decades of the 20th century. In this film, a brief meeting is shown during the film between Jobs and Gates, but Jobs' treatment of Gates appears to be one of disapproval. The film then proceeds to the collaboration between Gates and Jobs in which they develop the IBM PC, an important milestone in the advancement of the personal computer.