I don't have experience with these, but I have looked a little bit. There aren't a lot of price-friendly choices for the wireless cameras on the consumer market. Panasonic is one of the few. They have a set of components for the surveillance system, as you probably know. All of them use Atheros' 802.11 chipsets.
However, this camera is supposed to be used INDOOR. If you want to place it outdoors, you may be advised to house it in an environmental enclosure. Basically, this would amount to a plastic box (either clear or opaque). What you could do is make one using pieces of Plexiglas: glue them together and put some clear caulking around the inside edges. (Do this outside for the fumes, of course). However, you should have a lid for it so you can replace the batteries. The enclosure serves two key purposes: keeps the rain out, and it can be attached to a metal mounting bracket which then attaches to your house. There's still a possibility that the camera may have an earlier failure if the humidity level is persistently high in your area. Also, you may be voiding the warranty by placing it outside. It may be worth the risk, though. The alternative is to install a CCTV camera, which itself may be cheaper, but you'd need to do some invasive drilling through the house wall, and then either attach a SDTV video to 802.11 converter, OR route the video cable somewhere in your house. One key thing is to make it VERY difficult for someone to steal. I think there's a risk of that when you have a camera at a low height.
You mentioned the cold temperature. I think it's possible that it would prevent operation at some point, but I doubt it would cause permanent damage.
For the image security. They key is whether the camera uses the WEP or other types of encryption. This seems a standard feature with routers and pc cards, so I assume the camera would follow it too. Just make sure you check out the manufacturer's details to be sure.
http://customerproducts.atheros.com/cus ... eBasic.asp
(search consumer electronics and Panasonic to see the components)