SQLWebpedia

You can rename a stand alone SQL Server name and it is best covered in this MSDN article: http://msdn2.microsoft.com/en-us/library/ms143799.aspx  You can also rename a virtual cluster name, but not the instance name as that requires a reinstall: http://msdn2.microsoft.com/en-us/library/ms178083.aspx

I have done both with success in SQL 2005 and 2008. One thing to mention is you need to fully read the articles. With cluster virtual instance name changes, you must start with all instances on the same node and then fail them all over to each of the nodes. This will update all of the registry entries on each node. If you don't, service pack updates will fail and possibly other wierd issues will occur. Also, make sure to check DNS (including reverse pointers) and SPNs with SetSPN -L command.