Hi Mike,
That request gave me enough information to figure this out and I think others will find this interesting too.
It appears that what happened is that in the original attempt to install from the adCenter setup.exe the SQL server did not install correctly. Then when I uninstalled SQL from Add/Remove programs the uninstall does not actually uninstall it completely at all. It leave all the files in place, some of which then get in the way of a clean install using adCenter setup.exe.
The clue was in the log file.....
The system database file master.mdf already exists in C:\Program Files\Microsoft SQL Server\MSSQL10.ADCENTERDESKTOP\MSSQL\DATA.
So this is what I did.
Uninstalled SQL 2008 from the Control Panel
adCentre was not installed but I suspect if it is you should also uninstall it.
Then rebooted
Then I navigated to C:\Program Files\ and deleted the folder \Microsoft SQL Server\ and all of its contents.
****Word of caution here - I was 100% certain that Microsoft SQL Server was not installed prior to attempting the install of adCenter - deleting folders within Program Files is not generally a good idea. BUT... this is windows 7 and I could easily roll back:-)***
Then I ran setup.exe again and although it said it was "taking longer than expected to install" after about 5 minutes it completed the install and works fine.
Thanks for your help and hopefully that may help someone else.
Steve