Audio over HDMI - Dell Studio 1749

I just got a new laptop from dell over a warranty claim for my last one failing on me!

I can't get the audio to work over the HDMI out. The laptop just doesn't detect the HDMI cable, despite it being listed under the audio devices.

Intel® Core™ i3
Genuine Windows® 7 Home Premium, 64bit, English
4096MB 1067MHz Dual Channel DDR3 SDRAM [2x2048]
320GB (7,200rpm) Serial ATA Hard Drive
1GB ATI Mobility Radeon™ HD 5730 Graphics Card


I have never had an ATI card before so am new to the catalyst system, but Google has not yielded any suggestions on what I could look at. As a result I was hoping you kind folk might have some ideas? :)

Under Win7 on my XPS M1330 I need to force it out over HDMI through sound properties, did you give that a bash? Mine is a nvidia though..