You should check into the products that these people make at X10. They have a good product for a low price, and even if you don't know much about electronics, they will help you set it up over the phone for free. Plus they have a satisfaction guarantee!!
I use one of their floodlight cameras with a built in motion sensor in my driveway, and it stopped the vandalism that neighborhood kids were doing to my car. As a matter of fact I caught the two punks that were doing it.
Http://www.x10.com/sales.htm