Search by Zip Code and Distance

In CodeIgniter, what would be a good way to implement a search by Zip Code feature that also incorporated results a certain distance from Zip Code.

For example, a user might input their zip code and also select an option "Within 20 miles".

Then the results page would show results starting from closest to their zip code, and then list places further away ordered by distance up to 20 miles away.

There is an example on this page where it says: Search by Location. See  http://www.catholictherapists.com


On the example page, the location search also lets users search by city and state, and it has some auto-complete feature that starts suggesting places when you start typing a zip code ( and it says it is powered by Google).
Ideally I want to replicate some thing like this search by location, and the result page it produces.