Setup has detected one or more instances of SQL Server 2008 CTP1 on the computer where you are installing SQL Server 2008. ...

Setup has detected one or more instances of SQL Server 2008 CTP1 on the computer where you are installing SQL Server 2008. SQL Server 2008 installation is not supported side-by-side with SQL Server 2008 CTP1. You must install SQL Server 2008 on a computer that has never had SQL Server 2008 CTP1 installed.