I’ve been fighting an error trying to install SQL 2008 R2. The installer gives an error, “The SQL Server 2005 Express Tools are installed. To continue, remove the SQL Server 2005 Express Tools.” It turns out, the error was due to Red Gate SQL Compare, not SQL 2005. Thanks to this article, I was able to uninstall Red Gate to get SQL 2008 R2 installed.
http://sqlblogcasts.com/blogs/sqldbatips/archive/2008/08/14/sql-2008-install-blocked-on-express-tools-but-actually-due-to-sql-prompt.aspx