You can participate by turning off your lights from 8pm to 9pm on March 29th. You can sign up to participate on Earth Hour website, and while you're there you can learn more about the event.
There is some other interesting info on the site, including a carbon footprint calculator for Facebook (for those who have Facebook pages).
As for me, I might just participate with the Mountain time people. I get my daughter ready for bed around 8pm, and I don't see her taking too well to brushing her teeth and reading stories by candlelight.