SQL Data mapping webapp/server - please help.

Hi, I am doing a project at college for a web/mapping/sql based app, I do not know how to begin, and was wondering if anyone could help me out. Basically, I need an app where:

1. User selects 1 of 3 buttons on a website, which correspond to a lat / long.
2. When the user presses one of these buttons (the server side) will see the location mapped on google maps, and the SQL will do a search based on proximity, and list a result that is closest to its location. Say a restaurant.

How would I go about doing this? We need to preferable use Postgres SQL, which is a GIS, spatial sql software.

I have basic web design knowledge, and sql, our team needs to have a working example of this in about 6-7 weeks.

Can you guys recommend how to do this? I have an idea for the Web user side, but I have NO idea how to make it so that the server screen reacts to that which is pressed on the Website OR how to build a server based interface. I know oracle has some sort of GUI builder, but postgres SQL does not. How would you guys go about doing this in the easiest fashion? It needs to perform an operation that is basically: ((map lat/long, locate nearest feature to lat/long, return that feature information.))

Any help would be GREATLY appreciated.