The AnyExample.com website has a new tutorial today showing how to download files from the Amazon S3 service through PHP:

This is an example of non-interactive PHP script which downloads file from Amazon S3 (Simple Storage Service). Additional libraries like HMAC-SHA1 are not required.

You'll need at least PHP 4.1.0 or higher to follow along but the entire code block is there and ready for use. It makes the GET request to the bucket for your object with the correct authentication and opens a socket to pull the file down.