The key is behind using Streaming Technology .and this style is called Live Broadcast.
So what u need is Streaming Server , which receives video & voice from you Capture interface ( either PCI card or Pro device) and streams it.
The best Solution is done by either of these two:
1. Using Microsoft Technology ( Windows Server Media Server Service + media Encoder )
2. Using Real Technology ( Real Helix Server + Real Encoder 11 Plus )
you can find more information on Real Web site
MCSE + Security , CCNA , CCDA , CCNP , CCIE written