Just trying to add a third instance of sql 20005 to a server, run setup.exe ,the install warning comes up with the following 
"Edition Change Check"
"To change an existing instance of Microsoft SQL Server 2005 to a different edition of SQL Server 2005, you must run SQL Server 2005 Setup from the command prompt and include the SKUUPGRADE=1 parameter."
 
Errrr what  ?! I just want to add a 3rd instance but I only get the options to add components to existing 🙁
 
Deeply , deeply confused 
~si