Well I just thought i'd let you know how I got on. I've been a typical girl and gone for the first program I dowloaded, Tunebite.
I originally downloaded it from the link provided in this thread, that didn't work with trial MP4 conversion so I went to Cnet which promised a trial conversion with an older version download, that didn't work either. So I crossed my fingers and bought it.
Well anyway it works a treat, the only criticism is I can't seem to mute the audio when converting which is a pain cos I usually play music thru the laptop so have to convert in silence.
Thanks again for all your help.