When installing SQL Server 2005 you may come across an issue where MSXML6 and SQL Server Database Services fail to install. (See diagram below)

When SQL Server Setup tries to install MSXML 6.0 SP2, it detects that the version of MSXML 6.0 is already installed on the computer. Therefore, the validation process indicates that the current version of MSXML 6.0 should not be replaced. This stops the installation of both MSXML 6.0 and SQL Server 2005.

To resolve this click here