While attempting an installation of SQL Server 2008 I encountered a "Product" error very early during the installation. The product error searches on google claim that is has to do with a previous installation of SQL Server 2000 but that real issues is MSXML4.0. This version of MSXML4.0 is associated to SQL 2000 and must be uninstalled and MSXML6.0 SP1 install before an installation of SQL Server 2008 can be attempted on a machine. Even if you are attempting a new installation of SQL Server 2008 you get the same problem.
To uninstall MSXML 4.0 you can use this link.
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Databases
Microsoft SQL Server