Yes it might work, but from my text above it will all depends on camera resolution, FPS and bitrate. If the cameras encode into h.264 (streaming with rtsp) you can use hardware acceleration and the GPU on the graphics card which off-loads the CPU a lot.
Amount of RAM is fine. Amount of HD storage depends on how many recordings and retention time.
So add a couple of cameras at a time and notice how the system reacts.
-Henrik