Best bet would be to install a wireless (802.1x) camera and buy a wireless ADSL router. The Internet then transports the signal to another Internet connected computer anywhere in the world. If you wanted to avoid using the Internet there have been some surprising 802.1x distances recorded using Pringles cans - over 8 miles - but you will need line of sight to achieve this. The cameras are about 70 quid - give it a try - would be interesting to see if you can get it to work with a "high gain" antenna.