Charity Event Live Video Streaming, how do I stream live on the web?

I run fundraising events for a charity in the UK, and I would like to be able to broadcast an event live on the internet.

Please can someone tell me if it is possible to broadcast from a camera to a website so that the video can be viewed in real time? What is the technology involved? How powerful would the servers have to be to allow multiple users to view the stream?

So many more questions but don't know if this is the right place...