How can I convert .MTS video files to windows movie maker

[andrewaple]

I'm a novice at this. I have a camcorder that records in HD (?) with .MTS files on the memory stick. When I try to burn on to a DVD or use movie maker - as the shop recommended - the files aren't found/recognised. I can play them through media player - so they do exist! How do I persuade the computer to recognise them?
Thanks.