I think my life has just ended.
Tried installing and everything seemed fine. Fired up SSMS and got a message saying failed to register Class.
Unistalled a few times and re-installed - exactly the same.
Using Windows 7 Ultimate x64 with SQL 2008 SP1.
Don't know what I was thinking but attempted to upgrade SQL Prompt 4 to the latest version - this is now doing the same thing.
Can't wait to get it working and take it for a test drive.