I've read in releases by Square-Enix that since characters will be server side saved that the platform on which you choose to play (PC vs PS2) is irrelavent so long as you've got all your stuff installed and what not. It's virtually the same as going over to a friend's house and logging onto EQ using your account on their computer. This also promotes consumers to be more inclinded to purchase both versions than if characters were platform specific.

Leighton