Buy the new expansion from Steam, it will break your working version of FFXI.

I bought the new expansion set from Steam last night, got my codes in correctly and logged in on the working FFXI. I let Steam D/L its FFXI over night. This morning I came in to play and boom....My working version of FFXI WONT START! Next step, check the version that steam d/l'd. Its a fresh install with a nice 8 hour update attached with it. At the moment, I am currently moving a copy of the game from another computer that I dual box with and going to do an install with these files. I hope to Jeebus that this works.

I cannot explain how this happened but I do know from the Alla forums, I am not the only victim of this. Just in case you were thinking of getting your new set from Steam, DONT.