The closed beta for Final Fantasy XIV begins this Saturday, July 10. If you've been invited to test drive the MMORPG, there should be an email waiting in your inbox. It'll point you to the official forums, where you'll have to log in and find a link to download the client. Think of it as a multi-tiered quest.
The final version of Final Fantasy 14 will hit retail on September 30 in regular and more expensive "early access" versions.