If you're looking to copy a user from one environment to another, this Answers thread might be useful: http://splunk-base.splunk.com/answers/3426/copy-users-from-one-server-to-the-other.
If you are looking at a more complex distributed deployment, I suggest reading up on the deployment server, starting here http://docs.splunk.com/Documentation/Splunk/5.0/Deploy/Aboutdeploymentserver and perhaps more particularly http://docs.splunk.com/Documentation/Splunk/5.0/Deploy/Updateconfigurations.
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