APPARENTLY NOT EVERYONE in Silicon Valley slaves over a hot computer all day. From Hewlett-Packard in Mountain View to Apple in Cupertino, receptionists along California's computer corridor are killing time between cigarette breaks by wadding together discarded visitor name tags. It's not a recycling program. It's ""badge balls.'' The biggest balls -- some the size of monitors -- compete with keyboards for desk space. The most intricate look like they came out of a prison arts-and-crafts class. And now badge-ball building has become so popular that at Apple, where it all began, visitors are starting to slap their own tags onto the balls. ""It takes forever,'' says Silicon Graphics receptionist Harolynn Younger, ""then it gets really cool.''