Quote Originally Posted by Alpheus View Post
You dont need to reinstall FFXI to use the reg codes u get from steam. just start the downlaod and wait till it finishes it gets to 1% complete or so then pause the download and right click it. there should then be an option to view the codes that come attached with your purchase, paste them into a .txt file and then go to the SE account management system.

Go to service options located on the left hand side of the page and click on the blue button that says add a service and click FFXI you should then see a typical entry field for reg codes/cdkeys. After you enter the code you will be given the chance to choose which account to apply the code to so if u have multiple POL IDs make sure you use the correct one.
The OP is missing Expansions--entering codes won't grant access without installing the data. He/she also won't have access to the add-ons if the required expansions are not installed. So, in this case, an install will be required.