I've seen a few posts in these forums about people having VoIP and/or Voice
Chat issues with Vista. I just installed Retail (not Beta or RC) Vista
Ultimate and I'm having this issue too.

Here's the situation: When using a Voice Chat software title, such as Google
Talk, and chatting through a USB headset, the sound is fine unless there are
any other programs that use some CPU time. When other programs vie for CPU
usage, the voice on the VoIP application becomes distorted and completely
incomprehensible on both the sending and recieving end. Playing a full screen
game makes it real bad, but I can simply open a website and scroll up and
down really fast and cause the problem too. You only need to bump the CPU
usage up a bit.

The common response to the issue has been to update drivers (which I have
done, to no avail), but there have not been any real solutions posted. Also,
this problem does not happen in Windows XP on the same machine. On my
computer, when I had XP installed, I could have Google Talk open, voice
chatting with someone, and open any other programs and do HEAVY multitasking
with no sound issues or loss ever. In Windows Vista I can't really run ANY
other programs other than Google Talk or I risk sound corruption.

This is a serious problem. I have been testing vista since Beta 2 and this
issue has occured throughout all versions. I depend on the ability to use a
Voice over IP application, such as Google Talk, while using my system. If
this cannot be resolved, I'm going to have to reinstall Windows XP. I hope
someone can help. Thank you.