Development and Production Workflow

I've seen pieces of this problem solved around the net, yet I'm still confused, so I thought I'd ask the smart folks at Stack Overflow about this.

We're a small startup and at the moment our workflow from development -> production involves ftp-ing in and just uploading the dev code.

The dev code IS under subversion control - although we haven't leveraged trunks/tags/branches since I don't have a good idea of how to best use this structure. I feel that there should be a seamless integration with the live site that doesn't require me copy-pasting folders and files.

Here's some details:
- developing on CakePHP + MySQL
- hosted at Media Temple (gs)
- developers use both Mac OS (Coda) and Windows (Dreamweaver)

So my ask is: how do you setup a proper scalable workflow?