Have you contacted the manufacturer of the microphone and inquired as to
compatibility with Vista? Appropriate drivers? As has been posted once or
twice, Microsoft makes the operating system, and any third-party, whether
hardware or software, is responsible to ensure that their product functions
with the operating system.
Have you run through the microphone setup in the Control Panel? I found that
I had to click on 'Microphone Boost' in Microphone Properties/ Custom before
I could be heard.