Apple’s Boot Camp Assist 1.1.2 b includes SigmaTel audio driver for MacBook. However, when I first installed it, the microphone was not working.
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I first thought the microphone driver is not compatible with Vista. Later, I found that it’s not a compatibility problem. The microphone is just not enabled by default. Here is how you enable it.

Thanks a lot for this post!
I thought I was missing drivers, didn’t realise that it was such an easy fix!
This worked for Windows 7.
Thank You very much for this help !!!
A little effort for a great Help !
Have a nice day.
Clement,