I'm trying to remember how it worked with FFXI...but I "think" you had to buy both the Xbox 360 and PC copy to play on both. I might be wrong about this, as I didn't play very much on my 360, but I remember buying the all-in-one version for the 360 when I decided to play it on there at all. I know for sure you can't just buy the PC version and expect to play on PS3, but I think that's a given.