Ian, Thank you for your reply.
Things have worked out quite well. Putting the complete (with indexes etc) iTunes folder into My Music and then, in iTunes itself, adding the folder to the library, went ok. After that I consolidated the library but I suppose the files are in the correct place because no duplicate copying occurred.
Now in iTunes, my home videos (.mov) play in iTunes but some films I copied over (also .mov) have neither sound nor vision.
They play fine using vLan, so it seems that an open source application is better than Quicktime, which should worry Apple but probably doesn't
I know from experience on my Macbook, that even paying for the pro version of Quicktime did not give the required codec and one must download Perian and Flip4Mac before films can be played. I wonder if there is an equivalent package for Quicktime and Windows...