when you initially configure ffxi should have option to configure the specific keyboard. Try going through the setup menus w/ ffxi disk. For ps2 i think there's an option in the main playonline viewer menu, but i'm not sure how it would be for 360.
and when you say you can't play for 5-10 minutes w/out being interrupted do you mean that it kicks you off the game, you disconnect? Because that would be a problem w/ your router. I had to go through a series of annoying steps configuring my router for dsl before it would work correctly. For PS2 I had to set up specific ports to allow ffxi packets through, probably something along the same lines needs to be done for 360.
Good luck getting it working man, sorry you're going through all the troubles, but don't give up, it's an incredible game.