Recording video from security Wi-Fi web-cam: How Large An HD For Video Recording?

[vranswer]

Trying to figure out just what size external hard drive to buy in order to record security webcam video. My goal is to record video of the outside of the house using a wifi webcam and one of those shareware video screen capture programs. I would only need to keep the video if something happens around the house which we would want to see.

Is there a general rule of thumb for how many GB per hour a reasonably compressed 640X480 resolution video file uses? Would like to reset the recorder once per week and forget about it.