Cheap and easy if you have clear line of sight (Score 1)

If you have line of sight from roof to roof or from a TV antenna mast on either side: Buy 2 old linksys WAP11 v2.2 on ebay, 2 RP-TNC to N pigtail adapters, 2 flat panel or yagi 2.4GHz antennae and some 1" PVC pipe and elbows. Set WAPs to bridge mode. Disable unused antenna port on each device and connect antennae. Use some 1" white PCV piping to construct a basic antenna mount for each house unless you have a mast of some sort. If you use flat panel antennae, make sure you pay attention to the polarity markings and orient them the same on each side. You should be able to do all of this for about 150 bucks and have a reliable link for up to a few miles if you have clear line of sight. The high gain directional antennae are the key. Binoculars are handy when adjusting the antennae. All this does is "extend the wire", so as long as you hook the link into the 'router' on the broadband side, your Dad's PC will be directly connected his friend's network. The bridging mode makes it transparent and keeps it simple.