the passwords are hashed - but that's not the problem.
I gather that the currently logged in user is storred in a php session, so unless your game is hosted on DSiPaint you can't access that. (very easily >_> it seems like anything is possible if you try hard enough when it comes to this stuff...)
Anyway is there someplace I can check out your game? I have a simple PHP leaderboard script I could share with you.