Another common question on the forums, may be not a frequently performed task and as a DBA you should discourage in performing such actions. Microsoft SQL development team has already documented the information over the KBA 303774 and for the server name changes yes, you can change the name of an instance as long as the server is not clustered. Also for SQL 2000 version specific information refer to AA197071 link on the MSDN. Further the links for SQL 2005 version and specific to Clustered installations...(
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Read the complete post at http://sqlserver-qa.net/blogs/tools/archive/2007/10/02/rename-a-sql-server-instance-is-it-possible.aspx