When you download a mod, you should always start by reading the readme included in the download...
In this case stoffe's readme says:
3. How do I install it?
If you haven't already (since you are reading this file), unpack the archive this mod came in. Make sure the "Install Arena.exe" file and the "tslpatchdata" folder are located in the same folder, which should NOT be inside the game's override folder. Then run the "Install Arena.exe" file to install the mod. Just copying the content of the "tslpatchdata" folder to your override folder will NOT work. PLEASE READ THE INSTALLATION INSTRUCTIONS IN THE INSTALLER WINDOW!
Optionally, if you have the file "k_sp1_generic.ncs" In your override folder, move it out of there, otherwise the fixes to a bunch of force power related problems won't take effect. (Things like enemy Jedi opponents buffing YOU with their Valor etc...) This is not necessary to use the mod, but some force using enemies may be too easy or seem to behave in rather idiotic ways if you don't.
Also, you have to unpack the mod: a .rar file is like a .zip file. You can use winrar to decompress it.
For more info concerning mod installation and on where to get winrar, read this thread:
and you can edit your post by clicking on "Edit" in the bottom right corner of each of your posts instead of double posting.