Nathan Esquenazi wrote:
I am building a site which is a searchable directory of doctors.
Basically, doctors can register where their clinic is (address) and then
patients can search and find clinics.
Geocoding is the magic term you want to plug into Google. A quick search results in this http://geokit.rubyforge.org/ which may do what you want. There are many providers (free and commercial) of the postcode/zipcode lat/long details you will need as well.