It is pretty easy to convert a wireless to wired over a fairly substantial distance. You will need to purchase two of these...
http://www.dlink.com/products/?sec=0&pid=292
or something similar. You will put them into bridge mode. They will bridge a wired connection wirelessly. So...in the parents house, you will plug the output of one into the wired network or hub and in your buddy's place, you will plug the input into his router or modem. They key here is the multiple modes supported by this product. It is not just a router.
Hit me up with any other questions. The other was is to get a new N router...which will cover great distances.
http://www.dlink.com/products/?sec=0&pid=530
(that router is awesome) The signal will certainly reach that far. You could then use wireless cards in each PC in the main house. You may find that you need to use a repeater or extra antenna, which is no biggie. This solution does not allow you to use cabling...unless you got a wet.11 device for every computer you want to use the ethernet port on. Wet.11 are devices like this...
http://www.dlink.com/products/?sec=0&pid=333
They are mainly used for single devices like XBox or similar. It would be the perfect solution to whole problem if you could plug it into a hub and get IPs for all attached devices, but it does not give out IP addresses, it is only capable of 1.
Excuse any typos...I think faster than i type.
Tom