At a client I tried to install SharePoint 2010. It could not find my named instance of the database.
When I enabled Named Pipes, it worked however.
How to enable Named Pipes:
– go to your database server
– go to the SQL Server Configuration Manager
– Go to SQL Server Network Configuration – Protocols for YourNamedInstance
– on the right hand side of the screen you can double click on Named Pipes and enable them
check de Windows Firewall on the SQL Server