A few added details on the game were revealed in a recent interview with Japan's Famitsu magazine. It appears that the story for Promathia is a side story derived from the events leading up to the Rise of Zilart expansion. As mentioned in yesterday's update, the game can be played even by those who've never tried out Rise of Zilart, but the Square Enix representative interviewed by Famitsu suggests that players try out the missions in Zilart first.
Square Enix plans for Promathia to appear simultaneously on both the PlayStation 2 and PC in America and Japan, so you can rest assured that gamers in Japan won't have an advantage this time around.