Square Enix has released some information regarding the launch of the "Chains of Promathia" expansion for Final Fantasy XI.  Here is their official notice:

The release date and product info for the Chains of Promathia expansion pack are as follows: Release Date: Tuesday, September 21, 2004 (Simultaneous release for PlayStation(R)2 and Windows) Product Info: FINAL FANTASY XI: Chains of Promathia PlayStation(R)2 version: $29.99 (USD) Windows version: $29.99 (USD) Note: This expansion pack contains only the Chains of Promathia expansion data and is intended for users who already own FINAL FANTASY XI. It is not possible to play FINAL FANTASY XI using this product alone. For those who have not yet purchased FINAL FANTASY XI, we will continue to provide the original game, which includes the bonus Rise of the Zilart expansion pack. We will also begin service of FINAL FANTASY XI in Europe to coincide with the simultaneous release of Chains of Promathia in Japan and North America.