[Cecylia]

Okay, I found this somewhere, I hope it helps!

You need to download the model editor (found in this forum).
Each folder (the ROM folders in your FFXI directory) contains (or should contain) more folders
with specific .DATs. Simply select one that you personally
prefer. For the sake of argument, let's say you chose
the DAT for "Cloud's Sword From Final Fantasy 7". This is
for Great Swords wielded by Hume Males and Females. So in the modeler
select a sword that you'd like to switch.
To use the model
viewer, go into the folder marked:
"FFXI_Model_Viewer_-_Eng_v1-0-1"
Either hit "CTRL + A" or Select all items in the folder
(They're the same thing anyway), and then drag and drop
them into the root folder of FFXI, which by default should
be:
"C:\Program Files\PlayOnline\SquareEnix\FINAL FANTASY XI\"
And simply load the ".EXE" that came with FFXI Model Viewer.
(Note: If your FFXI directory isn't in the C drive, you have to extract these files there, then edit the model viewer's ini file to have the correct paths)
Once you've opened the Model Viewer, you'll notice off to the
right that you'll have some options as to sprites you want to
load. In the upper right hand corner, click the bullet called
"PC" (Player Character), not "NPC" (Non-Playable Character),
but "PC". In the drop-down Bar below that, select "Hume-M" for
your character race. There, below that, there should be
several more dropdown bars. Select the one with the subheading
"Main" (This is your Main Weapon), and go and pick [As an
Example] "G.Sword: Zweihander".
Once you do that, you'll notice a set of numbers in the upper
right hand corner of the Program's window. The number should
read:
"1-29-43.dat"
Basically, this is telling you the Location of the Sword's
image File. There are 3 "ROM" folders (they are separated by
expansion). The Folder marked "1" is the first "ROM" folder,
this is basically all the things in "Final Fantasy XI". The
"ROM2" folder is everything in "Rise of the Zilart", and the
"ROM3" folder is everything in "Chains of Promathia". Since
the DAT reads "1-29-43.dat", it's pretty much saying that this
DAT is located in the FIRST "ROM" folder, in the #29 folder,
and the 43rd "DAT" file. To be even more exact:
"C:\Program Files\PlayOnline\SquareEnix\FINAL FANTASY XI\ROM\29\43.dat"
Once you locate this file, either make a backup of it or put
it somewhere safe. Then open the folder that has:
"Cloud's Sword - Hume Male Only.DAT"
Take that file, and drag 'n' drop it into the ROM\29 folder,
and rename it to "43.dat". Then load up the Model Viewer, and
view the Zweihander again for Hume Male. If you did it correctly
then the Zweihander should look just like Cloud's Sword from FF7.
Note: Another easier way to view the .DAT locations in FFXI model
viewer. Either hit "ALT + S" or click on the "Settings"
tab, then select "Show DAT Number". That'll show you where
all the DATs are in the Dropdown Menu.
If you'd like everything to be back to normal, just reverse the
directions and switch the DATs back. Simple enough. I DO strongly
suggest you back up all your DATs just in case.