1. You cannot (legally) have an omni-directional antenna that does 1-2km. I don't feel like doing the math right now but that would be a REALLY, REALLY powerful antenna. You can however make/buy a directional antenna that will go that far.

Please see this informative, yet horribly designed, animation on how wireless networks work.

2. The example ebay listing given is obviously a hack job. There are wires that run into the LCD panel area to connect to antennas there from the wireless card in the bottom of the laptop. I am the maker just drilled a hole, put a connected in and re-routed one of the wires. It's a nice mod, good luck.

3. Just buy (or make) the appropriate length cable to go from the wireless card to the spot on the back of the laptop. Be sure to make sure you get the proper connectors (i.e. buy the antenna first).

4. It's pure mechanics, or rather antennas.

9dbi is a decent gain, but if your house is not even getting the slightest hint of a signal at all, you may just be SOL.

See http://www.usbwifi.orcon.net.nz/ for some nice and cheap directional antenna ideas.

-MLFnet