I've a Dell M4400 laptop and am using a DisplayPort to HDMI cable, but the sound just plays out of the speakers - not out of the attached TV. Does the DisplayPort support audio? Do I need a driver or something to get it working?
I spotted one forum post about this that indicates that yes, audio pass-thru is possible on the M4400:
You may need to disable the use of the laptop's speakers in the same control panel.