With the trial of a key finance official on Senator Clinton's 2000 campaign set to open tomorrow, a secretly recorded audiotape at the core of the case could prove embarrassing to politicians, political operatives, and wealthy donors to the Democratic Party. David Rosen, 40, faces three felony counts of causing the filing of false campaign finance reports in connection with a celebrity-studded fund-raiser and concert held in August 2000 at a radio executive's estate in the Brentwood hills above Los Angeles. Prosecutors have asserted that the true cost of the gala was more than $1 million but that Mr. Rosen...