O.K.
1. Add sabv.3do and sabg.3do to C:\Program Files\LucasArts\Jedi Knight\Resource\3do
if JK is installed on a diffrent drive change C to the letter of the Drive.
2. Add from saberyellow1.mat - kysaber.mat (all of the .mat files) to 
C:\Program Files\LucasArts\Jedi Knight\Resource\mat


Thats it you now can use the Buster Sword in the Single Player and in Multiplayer if the level has a light saber pick up.
I dont know if this works with other people that dont have it.  But if they do have it it will work.

Have fun

COPY RIGHT
I was the one who made it (son_goku80@go.com) and you will not say it is your own
The mats were made by someone else.