No audio with Windows 7

Question

OK everyone, I really hope you can help with this because so far this problem has completely defeated me.
I Just got a new Macbook Pro 17" and installed Windows 7 with Boot Camp. I have upgraded to 3.1 and updated everything I could but there is no sound at all from the computer when in Windows (OS X is perfect) and the red audio jack light is still on.
I have read that this is not an uncommon problem but so far have been unable to fix it. In Device Manager, I can see that under 'Sound, video and game controllers' there are 5 entries. The first says 'High Definition Audio Device' and the other four say NVIDIA High Definition Audio (I did not do this manually, but these drivers appeared after I installed the latest NVIDIA drivers for the graphics card).
I read on some other forums that the latest Realtek drivers solve the issue, but I downloaded and installed them and no change took place in Device Manager, so maybe the install went wrong somewhere?
In addition, I had problems with Windows 7 recognising the Broadom network adapter, and to solve that I was able to tell the computer to populate a list of drivers that I could then 'force' the device to use, but when I try the same with the audio hardware, it seems to work differently and instead of populating a list of drivers, it immediately asks me whether I want to proceed with the installation.
I'm really struggling with this, and I have been searching for answers in vain so I'm hoping someone can answer this once and for all.

Answer 1

As a follow-up to this post, I was able to solve the problem as follows:
Pre-conditions:
- Windows 7 (64-bit) installed with Boot Camp 3.1 Update applied
- Latest RealTek drivers downloaded and installed
- Audio combo jack emitting optical S/PDIF signal (aka "Red Light")
- No sound from laptop speakers
- No sound from headphone jack
- Device Manager showing 5 instances of "High Definition Audio Device"
Solution:
1. Open Device Manager and expand Sound, video and game controllers
2. Right-mouse-click and select Unintall for all instances of "High Definition Audio Device" (not sure if this step is needed, but I did it anyway).
3. Browse "Boot Camp" (Mac OS X Install DVD) \D:\Boot Camp\Drivers\Cirrus and double-click "CirrusAudioVista32" or "CirrusAudioVista64" (depending on whether you are using Windows 7 64-bit or 32-bit. I am using 64-bit Professional).
4. Proceed with installer
5. At this point, I checked Device Manager, and noting had changed in Sound, video and game controllers, so Right-Mouse-Click "Sound, video and game controllers" and select "Scan for hardware changes".
6. A series of driver installations will ensue, but most importantly "Cirrus Logic CS4206A (AB 71)" will appear under "Sound, video and game controllers".
7. Open the Sound Control Panel, and you should see "Speakers Cirrus Logig Default Communications Device" with a telephone icon next to it (Windows, you are so bloody obtuse....)
8. Right-mouse-click this icon and select "Test" - you should now hear a series of tones confirming audio is working.
9. I did not experience the same low levels described by OP, sound levels are loud and clear.
Hope this helps!!