On trying to install SQL Server 2008 on a system with SQL Prompt v3.8 or older editions, the installation can fail with the rule SQL Server 2005 Express rule that reads - "SQL Server 2005 Express Tools are installed. To continue remove the the SQL Server 2005 Express tools.''
Upgrade your SQL Prompt to v3.9 available in http://www.red-gate.com/products/SQL_Prompt/index.htm
SQL Prompt v3.9 is a recommended upgrade as it includes support for SQL Server 2008.
Red Gate Software Ltd