Thanks for the help Chris.
The article at http://learn.iis.net/page.aspx/624/ap... helped me to resolve the problem.
I am happy to report that all 4 sites are now up and running with version 5.2.3
I did appear to have a problem with two of the sites, they both came up with the following error.
Upgrading DotNetNuke
Current Assembly Version: 05.02.03
Current Database Version: 05.02.02
Upgrade Status Report
00:00:00.023 - Upgrading to Version: 05.02.03
00:00:00.272 - Executing Script: 05.02.03.SqlDataProvider Success
00:00:03.288 - Executing Application Upgrades: 05.02.03 Success
00:00:03.291 - Cleaning Up Files: 05.02.03 Success
00:00:03.296 - Updating Config Files: 05.02.03 Success
00:00:03.299 - Performing General Upgrades
Server Error in '/' Application.
I did appear to have a problem here but, as I was just about to restore the files, I refreshed the page and up came the site.
I then logged in and went to have a look at the version and it reported, to my surprise, 5.2.3 
The important thing that I found was setting the "permissions" on the site.
Adding the "DefaultApp" user seemed impossible at first, because it didn't exist when I searched for it.
However when adding the user I realised that it is important to select the local machine name from the "Locations" button and then copy in
"IIS AppPool\DefaultAppPool" (without the quotes) This then added the "DefaultApp" user to the list and I was able to give full rights to the user.
I hope this helps someone else.
Should I add my other query, regarding the disappearing Forums Module, in a different forum?
Regards
Roger