Episode 9 of "Sabrina, the teenage witch"
s01e09 Geek Like Me

Sabrina tires of Libby's constant teasing-- which worsens when Sabrina joins a science club-- so she gives the tormentor a taste of the taunting by turning her into a nerd. Meanwhile, Zelda wants Hilda to throw out some very old items (such as a suit of armor and a cannon). Tired of watching Libby treat people badly, Sabrina decides to give Libby a taste of her own medicine by transforming her into a geek. However, when Libby succeeds in turning her fellow geeks against the entire school, Sabrina must find a way to unite her classmates before the plan backfires. And Hilda triumphantly uses her antiques against marauding snowballers.