An error has occurred while establishing a connection to the server. When connecting to SQL Server 2005, this failure may be caused by the fact that u

If you're having any issues doing an install on Vista and you encounter the error:
An error has occurred while establishing a connection to the server. When connecting to SQL Server 2005, this failure may be caused by the fact that under the default settings SQL Server does not allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server) (Microsoft SQL Server, Error: 2)

Try the link below to resolve that issue.

http://littletalk.wordpress.com/2008/03/21/an-error-has-occurred-while-establishing-a-connection-to-the-server-when-connecting-to-sql-server-2005-this-failure-may-be-caused-by-the-fact-that-under-the-default-settings-sql-server-does-not-all/