Final Fantasy XIV, then a gameplay demonstration from GamesCom 2009 will likely provide an answer: One of the games has a "V" on the end of its title, while the other doesn't.
Okay, okay, there's a bit more to it than that. In the gameplay demo -- which was captured by GameVideos and posted after the jump -- we can see the biggest difference right away: The game's combat system has seen a major overhaul. Gone is the weird drop-down menu system, which looks to have been replaced by a much more streamlined hotbar, as seen in the whack-the-obese-chicken footage. Also, FFXIV looks absolutely stunning. That's not much a shocker, though, considering Squeenix's pedigree -- a history that includes beautiful-looking games and an inability to count sequentially.