If you have a clear line of sight then you could use a combination of
HiGain antennas. A combination of 9dBi (omni) and 14dBi(directional)
could give you a point to point connectivity of approx 1 mile.
You will need two wireless bridges at two ends to connect antennas.
The Linksys 54G wireless access point can be used as a bridge also, so
you can make a link between two buildings.
Once you hav elink between two locations, you can connect it to the
local routers at both ends (need not be wireless). This is just one
option. Another option is to use just an wireless router (or access
point if you already have a router) and attach a omni directional
antenna.
You can find the details of antenna at
www.hawkingtech.com or
www.netgear.com or search for Hi Gain antennas.
Hope that helps.