Go to C:\Users\*YOUR USERNAME*\AppData\Local\Activision\CoDWaW\Mods (you may have to turn on hidden folders in order to see it or you may have to create that folder).
Insert 'iw_28.iwd' and 'iw_29.iwd' there.
Go to *YOUR DISK*\Steam\SteamApps\Common\Call of Duty World at War\Main.
Insert 'codlogo.bmp' and 'd3d9.dll' there.
Change the name of 'codlogo.bmp' to 'codlogo (2).bmp'.
Go to *YOUR DISK*\Steam\SteamApps\Common\Call of Duty World at War.