OK. Hopefully you’re all reading this stuff BEFORE trying to do the install and certainly BEFORE uninstalling everything in sight. The latest version of SQL Prompt, version 3.9, is 2008 compatible AND doesn’t cause this problem with the install.
So, I’ve got to reinstall the software. Time to track down my license. I hope I kept that email.
At the risk of necro-posting but with the hope that somebody searching for solutions to the same problem will find their answer: I didn’t have SQL Prompt installed. However, I did have SQL Server management studio express installed. Having uninstalled this I managed to install SQL Server 2008