according to Wikipedia (http://en.wikipedia.org/wiki/IEEE_802.11
) an 802.11g connection has a range of about 140 meters.
a quarter of a mile is 400 meters.
it's not just the base station that you'll have to fit a big antenna to but also your recieving computer (as that transmits as well).
you can use certain areials (google Cantenna) to increase the effective range as these act as amplifiers, focusing the signal in a single direction.
you'd use this to share wifi between two fixed locations.
not exactly sure of the distances achievable though.