Why not Supported in Old Version?

Paint.NET not supported Windows 2000 or earlier versions
http://blogs.msdn.com/rickbrew/archive/2004/11/03/251890.aspx

MSDE will not be supported on Windows Vista
http://blogs.msdn.com/sqlexpress/archive/2006/08/09/693650.aspx
http://www.microsoft.com/japan/sql/prodinfo/previousversions/faq-sql_on_vista.mspx