are you on sp3? if so run a repair install with an install disk with sp3 slipstreamed, since movie maker is integral to windows, it cannot be downloaded separately from what I have read, and in a clean install all movie maker files are there so a repair install will do the same, BUT if you only have an sp2 install disk and you do a repair install it will repair to sp2 and you will have to install sp3 over again and all your programs, so I would not do this unless you have an sp3 install disk,
or if you know exactly what files are missing and I have them on my xpsp3 professional pc I can upload them to my one drive for you