bfig

I'm trying to setup a usability lab and bought an Annke video surveilance system. I have two rooms, both with two cameras and NVR and I want to be able to see Room 1's cameras on Room 2 and vice-versa. That I already solved. Now my main problem is I want to be able to see what a user is doing on a PC and feed it into the NVR as if it were a camera. Ideally I would be able to see on the NVR, simultaneously, the feed from two cameras and the PC's desktop. To do that I need to convert the output of the PC and feed it into the NVR just like if I were connecting it to a projector. The output from the PC is VGA. So how can I I convert this signal into the right signal and feed it into the NVR over its POE connection? Thank you in advance.