For new players who have never installed and played: Download the official game from the following link and install it once the download is complete  Download Installer Final Fantasy Xi button at the bottom of the page.

As a second step you will have to download one of the three clients made available (read the mini installation guide inside the rar file) to be able to play on the private server in the link below in the description. Be careful adding the server profile and the xiloader in windower if you are already a player of the official version it does not compromise the functionality of the original game in any way! (if you already have Windower do not install it again)  If you are already a Final Fantasy XI player and already have an updated client and windower you will just have to download one of the clients made available for you! (follow the instructions inside the zipped files)  Ahita V3 , Windower 4 , Fairy Custom Launcher 2.0 (beta) Download buttons at the bottom of the page. 

As a third step (again if you don't already have the game installed and updated) you will have to download the already updated client prepared by me in the link below in the description (the client you will download has the HD Game Maps mod) once downloaded you will have to extract the folder, then you will have to copy the playonline folder to your existing one installed on your computer and overwrite it: Button at the bottom of the page. Download Client Update button at the bottom of the page