Windows 7: Question on Mic for voice software on 7

I would like to know if I'd be better off with a usb microphone.
Hope that does not sound like a silly question. But I'm now settling into 7 x64 and would like to use the voice software it has. With XP I used Nuance for dictation, launching software and IE. Nothing that intense but if 7 x64's voice software works out it would be advantageous.
I have a half way decent desktop analog mic. Under 7 it picks up more background noise and feedback if I use any boost. And so to get any decent green in the bars I have to be within 6" of the mic. Ok it's not the quietest home build in the world, but it's not bad either.