Try going to The Metropolitan Opera homepage - in addition to ticket sales, radio broadcast schedules, and an extensive shop, they also have an excellent history section

You could also visit the New York City Opera company

Other online companies include the Boston Lyric Opera company, and the L'Opéra de Montréal.

OperaRadio is an excellent streamed website that allows you to listen to opera radio stations on the web - beware, this link hogs bandwidth - don't visit during regular school hours.

Finally, Operabase is an excellent resource for links and references to the genre.

Other sites, such as BBC Classical Music, offer articles on classical music in general. BBC Radio 3 is an excellent streamed music channel that plays classical music and provides resources.