Reducing graininess in zoom videos

Hi all,

I am lucky enough to have lesbian neighbors who occasionally walk around their apartment naked. Unfortunately they mostly do it at night, by the light of their bedside lamps. I have a 10x optical zoom HD video camera which is able to film them, but it is a little grainy. I have installed Avidemux to crop the video, but can anyone explain to me how to get the best effect out of the various filters to sharpen the image without reducing the (already limited) quality?

I will of course share the results for your viewing pleasure :)

Thanks!