What is group velocity and why doesn't it allow FTL communication?

[Stylesjl]

I tried reading Wiki on what group velocity is, but the description was very hard to understand, although they did state that group velocities have managed to go faster then light in a vaccum (but no communication is allowed). So what is group velocity, and what prevents classical information from being carried in it?

 

[Perfection]

Group velocity is the velocity of an amplitude peak of some waveform, this does not have to be the same as the signal velocity:

Here's a good java applet on it because it's late and I can't communicate crazy analog stuff well.
http://gregegan.customer.netspace.net.au/APPLETS/20/20.html