thanks very much guys. After reading this I remembered I have access to CS5 at work so took in an SD card full of 4gb files totalling 1hr 40 mins.
I copied the PRIVATE folder from the card to the desktop and imported into CS5 and although it shows each of the 4 clips in the project window, the length on all of them is 1hr 40mins.
When I drag the 1st one into the timeline it is 1hr 40mins so it obviously joins them all which is great news.
I did some more tests and moved them out of the default file structure (PRIVATE – STREAM – etc etc) and found they still worked.
When i renamed the files they did NOT attempt to join and interestingly when I renamed them back to what (I think) they were originally they still did not join automatically.
All in all, well done CS5!