On
www.vatsim.net
If you want to try flying - look at the links on the left hand side called Pilot resources.
If you fancy being a virtual controller - have a look on the right hand side of the main VATSIM website, it lists all the regions. Once you go to that regions website they will have information about how to start the process. Most have good quality training material etc to get you started.
Maybe we'll see you online.
TV