Assumming that you have downloaded the client and extracted it, follow below steps that I modified to suit Windows 10:
Step 1: Get ready to install Final Fantasy XI! Grab a sandwich and beverage and sit back and relax.
Here we install the game, pretty basic stuff.
Step 2: 32-bit users launch FFXISETUP.exe and install everything.
64-bit Windows users launch 64bit POL, then launch FFXISETUP.exe and install everything EXCEPT Playonline
These steps let you update the game via the check files option.
Step 3: Open the update files folder, and select all the files and copy them
Step 4: Open the directory you installed into, for example:
C:\Program Files\PlayOnline\SquareEnix\Final Fantasy XI\
Step 5: Paste the update files you just copied into this folder. Click overwrite on any duplicates.
Time to update the game. This can take hours. You can idle in http://nasomi.net to pass
the time, or go to http://nasomi.com and read "Getting Started" or "Controls" to brush up
Step 6: Launch PlayOnline, it will briefly update, and then restart. This can take 20-60 minutes, depending on your internet.
Step 7: Click "Existing Members" and enter POL ID ABCD1234 and click register, then click login.
(nothing else needs filled in, this isn't the actual login)
(Don't actually log in, just register.)
Step 7: On the left side click "Check Files" and CHANGE THE DROPDOWN to read FINAL FANTASY XI.
If you DO NOT see FFXI in the dropdown, see step 3.
Step 8: Click "Check Now", this process can take 10-60 minutes. Eventually it will come up with "Repair". Select that. This can take a few hours.
Step 9: Open your POL install directory to find and copy the 'data' folder.
(typically c:\program files (x86)\Playonline\SquareEnix\PlayonlineViewer\)
Step 10: Back out and open your FFXI folder and paste the data folder into this directory.
(typically c:\program files (x86)\Playonline\SquareEnix\FINAL FANTASY XI\)
Step 11: Open the "Visual C++ Runtimes" folder and install ALL 4 files in the folder.
***If it says "Repair", you already have that one and can move on to the next.***
Step 12: Open the "Ashita" folder from installer's folder, right click Ashita and run as administrator.
Step 13: Click on one of the Nasomi server profiles and right-click and choose edit to suit your preferences, or double click to launch. Remember to allow on firewall when there's windows's firewall pop-up
Step 14: Choose 2 to create a new account, then 1 to log in with the account you created.
Step 14: See you in game!
Notes:
Each time you want to play, run Ashita.exe as administrator.
To log out, type /logout
