Sony Computer Entertainment have released a small update for the PlayStation 3 that allows PlayStation 2 games to store cache data on the hard disc drive, like Final Fantasy XI or the SOCOM map pack. Rather than a regular system update that would up your firmware version number, the update is a standalone package available on the PlayStation Store.
The update runs nearly 7MB in size and basically looks to create a virtual space for PS2 hard drive support. PS2 games that can use, or in the case of Final Fantasy XI, require the hard drive will simply prompt you to save the data as per normal. On the PlayStation 3, this data chunk is listed under the Game Data Utility like any other cache information would be, though it's all stored in a single piece of data.
So for those of you who want to try out FFXI on the PlayStation 3, now's your chance.