Copy office.wmp and gun.mdl inside your game folder (work if you are using the templates) and weapons.wdl inside your template folder (overwrite the existing weapons.wdl file). Build the level and run it, then pick up the gun.

The gun was created by Matthew Swansson aka Lensflares and was downloaded from Acknex Unlimited
You can contact the author using Lensflares@Yahoo.se