"I love beautiful clothes," says actress Catherine Oxenberg. No surprise coming from an alumnus of TV's fashion-steeped "Dynasty." Until now, Oxenberg--like many women--hadn't considered sturdy, utilitarian denim part of any high-fashion equation. But this spring, European couturiers are letting the jeans material lend a casual crispness to sophisticated designs. The result: a look that Oxenberg calls "urban earthy." Oxenberg's next project is a departure from the glamour-girl milieu: "Waxwork," a big-screen comedy spoof on horror pictures.