I've seen some articles on how to use WMI to manage SQL2000 servers (after installing SQLWMI80.msi manually) but I've not seen anything about this for SQL2005 and SQL2008.
Has this been depreciated? Or is WMI now installed as standard with 2005 and 2008?
The preferred method is to use SMO
Yes see SQL Server 2008 Books Online (June 2009)WMI Provider for Configuration Management Concepts this also provides the links to the 2005 version. But you'll want to use SMO instead. 2008 also has a powershell provider.