I think I have managed to get most of the answers to my queries.
I have been experiencing "codecs" errors when using my windows media player (running Windows XP) but from a few searches, the simplest way to overcome the problems was to download the VLC player (done

).
However, when I tried to watch a film which I had previously saved (checked before and was working fine) it still opened it up in WMP and the VLC appeared as another option at the foot of the screen.
Further searches reveal that VLC will not open the film by default- that remains with WMP but the suggestion was to open the saved file/film, "outside of Lime Wire" and then use VLC to open with it.
This is the bit I am still unclear on.
I am quite happy to leave WMP as the default and watch a film when it runs OK, but if I get further codecs errors, I'd
then like the option of using VLC. Or perhaps I can set VLC as the default?
Unfortunately I am a complete IT numbnut and so require simple instruction- I appreciate this may take a little longer but I assure anyone kind enough to help that it will be gratefully appreciated.
I hope I have stated my problem clearly enough but I'm more than happy to answer any further questions here or via PM.
Thanks in advance and top site by the way- well impressed.