Weatherproof Security Cameras

Hi, I am trying to set up a home security system using five webcams and I am tyring to follow this tutorial.

http://www.simplehelp.net/2006/09/27/how-to-use-your-pc-and-webcam-as-a-motion-detecting-and-recording-security-camera/

But, The distance from my computer to webcam is almost 20meters.
How can I extend the length of my webcams up to 20meters?
If extending the cable length is not a good idea, how can I set up webcams wireless?
Please help me.

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