A new group called the Frog and Peach Theatre Company is combining what used to be disco with what used to be Shakespeare... sort of. It seems that for their upcoming version of "Richard III", running at the WestPark Church (165 W. 86st St., 866-7280) from Sept. 26 to Oct. 20, they've recruited Karen Lynn Gorney, who played John Travolta's love interest in "Saturday Night Fever", to play the role of Elizabeth. Gorney has made quite a name for herself in the last two decades since "Fever" was hot, and anyone who hasn't been chronicling her activities over the last few years has really missed something. There's no excuse now; admission is free.