How would one–in theory–go about getting free internet service by accessing my neighbour’s secure wi-fi?

Though I’m not sure which neighbour it is, I’m certain they work hard for their money and would not want to suffer the teensiest, tiniest, nearly unnoticable loss of bandwidth by sharing their wireless connection with anyone else, even when the hour of day suggests they themselves are not using it at all. I will rest easier once I discover an easy way one might leech oneself onto their service and get free internet access, allowing me to blanket the neighborhood with flyers advising this unknown character of this weakness in their security. It would be particularly alarming if their were some handy, convenient key-gen program available which would make it easy for someone to gain access, even if they, much like myself, had only a limited knowledge of computers.
I know what your thinking: wouldn’t any good christian gladly share with a neighbour, us all being brothers? Yes, of course they would, but we must respect their decision, however misguided, to prevent access to others, however needy or well-meaning.

If the neighbors are using wep there are several good wep crackers that can be found. Some even run on windows! If using WPA that is a different nut to crack! Of course most wireless routers will revert to factory settings if the reset button is held down for 30 seconds, opening up the network to the world. So the smart neighbor will have used WPA and secured his router away from prying eyes! As many neighbors are not this smart, the use of a high gain directional antenna will sometime reveal the neighbors with the lesser capabilities allowing the squirrels to fill their coffers.