Right now, there's only one way to get an early hands-on with Final Fantasy XIII: own the Japanese Blu-ray release of Final Fantasy VII: Advent Children Complete. Heck, you can't even go to a gaming convention to get a proper hands-on!
Square Enix is undecided about releasing a playable demo of Final Fantasy XIII in the States, but if it does, it won't be available on disc form. Square Enix's Yoshinori Kitase commented, "we are thinking of providing it in a downloadable format," reiterating earlier sentiments. However, don't expect to play a localized version of the PS3 demo. Instead, "if we were to provide the demo overseas, it would be a completely new version." The game has progressed quite a bit since the release of the Japanese demo, meaning Square Enix would be more inclined to show something new ... if they decide on actually making one in the first place.