Have one of these modified Microsoft HD cams ourselves, not used it much, but to the point, here is a reference to some software that you may like to look at, still unable to adjust the gain - but that seems to be a feature in the camera.
I have no connection to the software other than its on my netbook and I also 'lurk' on the UK astro forum that prompted it.
Hope this is useful, Mick
https://sites.google.com/site/rwgastro/sharpcap