Can I use my PC and my USB microphone for 'live' commentry during a PowerPoint presentation?

I know I can record commentry which can be saved and played back with the Powerpoint presentation; but there doesn't seem to be any programme available which would allow me to use my PC as an amplifier in 'real' time. I just don't want the hassle of carrying around a seperate amplifier for doing the commentary.

While nothing specific comes to mind right this second, the reason there usually aren't any programs to do what you're describing is because, well, take a laptop for example. The microphone is built into the computer, as are the speakers, so as the speakers would resonate the computer with the sound waves, and the microphone would pick that up, thus you get feedback, and trust me, that's the last thing you want during a big business presentation. I have experienced in many cases where simply plugging an external microphone in will cause the computer to, as you say, act as an amplifier. Something you might want to try is simply adjusting the sound levels. Right click on the volume controller and select audio properties (or something along those lines) and adjust the input and output sliders till you hopefully hear something. As for software to force this effect, I could only imagine it as being pretty seedy stuff.

*edit* I just noticed you mentioned a USB microphone. I have never experienced a situation that would allow such a thing because the problem with USB microphones is that they take over the audio controller of the computer making the USB microphone the primary audio device. So it is possible, though very unlikely. Honestly? You're probably best off setting up a small net-book in the corner of the room, and use the USB microphone and skype to call the main laptop that you're using for the presentation, and have that one hooked up to the sound system. Seems a little ridiculous, but it would be very effective.

I am looking for a solution to the same question here. I want to use a bluetooth mic during my presentation allowing wireless mobility. Yes, I would stand up and walk around a bit without having to hold a mic because those bluetooth headsets can easily be clipped on. This would be great for a lecture, too. I don't have to prepare a another set of wireless microphone.