Alright i personally have not set up wireless at home but i have set it up briefly at class, now these neighbours how much knowledge do they have of computers? You may not need to apply much to stop them, anyways to the point, i would start by applying a mac address filter, what this does is only accept connections with the certain mac addresses of your nics wanting to access the network and also apply a wep encryption or better yet WPA encryption. Sorry i cant tell you how to specifically do these, its just that i dont have that much knowledge of it, thats all.