When I start WinSCP and get the Login box, I select New Site node on the left. When I check the Protocol drop-down, I only have SFTP, SCP, FTP and WebDAV. I don't see Amazon S3 as an option.
I am currently running version 5.11.3 (Build 7995). When I do a Check for Updates, it says I have the latest version.
PS - Nevermind. Upon digging a little more, I see that S3 is only available in the beta. Downloading now.