ASUS K8V Soundmax AD1980 driver for Windows Vista

I have a ASUS K8V motherboard. It has Soundmax AD1980 on board sound card. After installing Windows Vista x64 I am not able to hear any audio. I am having a 2.1 speaker which was working before. When I had performed Vista setup, the AC97VIA sound driver was installed automatically. Upon reboot the system showed up some audio. There was audio on my speaker but there is no sound from S/PDIF. I had done a number of installation of Vista 64bit drivers but it does not work. While looking on web I found that it needs some kind of smwdm.sys file which is responsible to run the audio. It is not found. Is there a way I can download it. One thing I want to mention more here is, that this thing works quiet well on Windows XP x64 system.

You said that it is working well on Windows XP 64bit but not on Vista, then it simply means that your system is not compatible with the same. You must avoid using Vista here. Or try to find the 64bit working drivers. Did you tried to install the drivers in compatibility mode. You can test that once and that will be the only last option left for you.