Right now we're in Beta Phase 4, so the forums are getting congested like crazy. Here's the link to the client download, as per the "apology" page for the congestion.

■Downloading the Client
The game client is available for download from the following URL.
http://sqex.to/FFXIVGame
Link to the beta forums: http://forum.square-enix.com/ARR-Test/forum.php

In regards to your question about the game for sale, there were physical Collectors Edition PC and PS3 games, but those were produced in limited quantities and sold out. Right now the only thing you can pre-order is the standard edition PC or PS3, your choice of physical disc or digital download.