Inside of PAK000 (you can open it with winRAR or something of the likes) there's a folder called def. Find "weapon_pistol.def", extract it, open it with notepad and look for a piece of code that looks like this:
model viewmodel_pistol { mesh models/md5/weapons/chaingun_view/viewpistol.md5mesh ...}
Underneath mesh, type offset. Then type ( 0 4 0).
The resulting code should look like this:
model viewmodel_pistol { mesh models/md5/weapons/chaingun_view/viewpistol.md5mesh offset ( 0 4 0)}
Save it, then go to your doom 3 folder, go to base, create a folder named def and put the file in there. Or if you're using the game with something like sikkmod, just put the def folder in the mod directory.
Hope this helps! Heh, Doom3world had to babystep me through this. As for the script, http://files.drdteam.org/index.php/files/get/WBsLGnkBHX/weapon-pistol.zip.
Just create a "script" folder in your base/mod directory and put it there. Hope that helps!