Unpack the mod folder in the rar file to where your Battlefield 2\mods\ folder is at.
A shortcut will be there named combat remember to edit it out so it can match your game localisation which is very important for it to work.
"C:\Games\Battlefield 2\BF2.exe" +modPath mods/Weapon_Mod2 +menu 1 +fullscreen 1
and Start-In change in to this
This mod works only with BF2 1.41,1.50 versions.