Whenever a new file is added to the project, Xcode adds the following lines of comments on top.
// Created by {my name here} on 8/4/11.
// Copyright 2011 _
In Address Book select yourself (or add yourself if you aren't there) and then go to Card -> Make This My Card in menu bar. The name, last name and company name from that card will be used to populate info in file headers when creating files from Xcode templates.
Alternatively, you could set it using defaults via Terminal.app like this:
defaults write com.apple.Xcode PBXCustomTemplateMacroDefinitions '{ORGANIZATIONNAME="ACME Inc.";}'