Below are a collection of links on how to rename a SQL Server server.
Rename the SQL Server engine. This describes how to run
sp_dropserver 'old_name' go sp_addserver 'new_name', 'local' go
Rename SQL Server Reporting Services server. This describes how to update a config file with the new server name.
Correct an issue with SQL Server SP2 and Sysprep. This is needed when you run sysprep to rename the machine. The short of it is you will need to delete some registry entries.