Alright, I did exactly this, and I'm running into a problem.
POL loads up fine, update went through no problem, but when it tries to launch the actual game, it gives me the FFXI-9001(-1) error for invalid installation path. I've triple-checked the reg entry and the path is definitely pointing to the correct location, so I dunno what it's throwing a fit over here. Gave me the same error with windower and without.
XI Wiki



