The following is the link official to download the Final Fantasy XI: Ultimate Collection Seekers Edition which has the entire game client. You need all 4 files fully downloaded before continuing.
Run the "FFXISETUP.exe" and follow the instructions for install, make sure all of the boxes for the expansions are ticked. DirectX 8.1 is not needed (unless for some reason you don't have DirectX). Be aware the installation needs 5 GB of space for the temporary files, and 10-13 GB for install depending if your drive is compressed.
In the download below, there should be a zip archive telling you to do this step before running PlayOnline. Extract the files to "\PlayOnline\SquareEnix\FINAL FANTASY XI".
Start up PlayOnline. It will ask you to patch. Do it!
After it has patched it will restart.
Once it has opened it will ask you to either register a new account or login as an existing member, choose existing member. Choose a member name. Then for your PlayOnline ID, put ABCD1234 (In caps). Select Register.
Now you need to update Final Fantasy XI to the correct version.
To do this, go to the main login screen in PlayOnline, there should be a list of options on the left. Choose 'Check Files'. There should be a drop down box, select Final Fantasy XI (Version should be read as Unknown) and follow the instructions to check the files. After it has finished, there should be some files that need to be 'repaired'. Click on repair files and this should update your client to the latest version.
After the update has finished, copy the data folder at PlayOnline\SquareEnix\PlayOnlineViewer\data to the Final Fantasy XI directory at PlayOnline\SquareEnix\FINAL FANTASY XI. Afterwards you should have the directory PlayOnline\SquareEnix\FINAL FANTASY XI\data.
Adding a Booter to your Client
There are two booters to choose from:
For Ashita V3:
Click here: https://drive.google.com/open?id=1r2JU6UWfSWOU1q3UX0hp2pdMqitenHhg
Place the file you downloaded to where you choose.
please also remember to download x86 and x64 from here and install both https://www.microsoft.com/en-us/download/details.aspx?id=48145 here.
Run Ashita.exe as an administrator.
Edit the NIGHTBROOD configuration by clicking the pencil. Replace --user yourusernsme --pass yourpassword in the line "Boot Command". Go to the Window tab and set your desired resolution in both FFXIConfig and Ashita V3, they MUST match!
Click the save button then click the Arrow!
For Windower 4:
Refer to this post. http://nightbrood.freeforums.net/thread/172/setup-windower