I'm running Ubuntu 12.04. This is the strangest problem ever and I have no idea how to describe it, but I'll try. I got the audio working with the HDMI, and then it shows my Ubuntu desktop on the TV screen but does not show any programs I have open? It sometimes shows my mouse, but only if it's on the sidebar, and only sometimes.. Weird right? Anyone know what's going on?
Ubuntu by default uses the 'Extend' configuration when connecting to an external monitor, this configuration basically extends your screen. I think that if you hold Alt when the mouse is at the edge, it'll cross over to the other display. You can use this to move a window over to the other display.
You can make it clone the displays by going here
System Settings -> Displays
and changing the settings as you like.