l understand your situation, but to be able to help you I need some technical info. What brand and model number is your router? What is the brand and model number of your wifi on your PC? What kind is it (internal to laptop, USB, PCMCIA, PCI card, etc)? Do both wifi adapters have external antenna connectors, if so what kind? What is the approximate distance between the two? What obstacles are between the two? What's your budget?
The key to remember is power is better than sensitivity anyday. There are routers available with up to 2Watts (most are 100 to 200 mW) and there are PCMCIA cards available with up to 500mW. There are also external amps available in a wide range of power levels.
A normal 8dB antenna like what I have on my router is 1 1/2 in in diameter and 24 ln long. Those antennas you linked don't even come close. They are designed for indoor use, don't have nearly the output nor sensitivity as a good 1/2 wave antenna such as mine and if location is a problem will probably lose half their capability with a short 20-30 ft cable. The can antenna is a good idea - using 2 aimed at each other would be better. I also incorporated a 24dB directional antenna in my system, but its a pain to aim because it has such a narrow beam.
Answer the questions above, figure out what power you currently have, guestimate what power you think you need and we can go from there.