I've had this system in mothballs for about a year and a half. The OS it had on it was the 32-Bit Beta of Windows 7. I broke it out to turn it into an HTPC. When I first broke it out it worked just fine including full audio and video capability. I installed a full copy of Windows 7 Ultimate 64-Bit and Service Pack 1 to use this system on a regular basis. Now, the only audio I can achieve through the system is a high-pitched hissing and clicking and warbling instead of producing the proper sound. I've attempted several different types of drivers including the ones from the ASUS website and the ones from the Realtek website (attempted both w/ and w/o the hotfix). I've attempted HDMI Audio through my video card (which worked on the old OS) and through the normal jack in the back. Both produce just the aforementioned hisses clicks and squeals.
Motherboard: ASUS M2A-VM
Video Card: Powercolor AX 4850 (Radeon HD 4850)
Ram: 4 GB
You are very welcome. Hopefully you will not need to replace the MB soon, but if you do, you can take the sound card with you, sell it on ebay, give it to a friend for a birthday present (all my friends are geeks )
Please post back if you need any further assistance.