I'd like to connect an Amazon RDS (Postgres) database to a force.com instance via something like "External Data Sources".  Not having any luck as no connection type (ODS, etc.) appears to be working...  This is for a custom application (built over the past few years) to have it's data to be administrable by a new Force.com user interface.  

I have built out a cakephp application that is hosted on AWS and am now looking to build a force.com app that connects to the same database and provides some of the (relevant) functionality to clients who have a salesforce account.

 

This will be my first project in force.com and I'm not sure exactly where to start. Should I just use the IDE, and if I do that can I build an app using an existing mysql database not hosted at force.com?