MovieMaker running under Vista Home Premium

All the softward came installed by Dell; I’ve successfully used Movie Maker, whatever release came with Vista Home Premium. Now when I attempt to open the saved files, which have been saved and opened numerous times in the past, well I get an error saying 'something like' the version of MovieMaker is different that the version used to make this file...along with a red x indicating it’s not gonna happen.
I haven’t loaded the new service pak for Vista, trust be told I feel like Vista is a turd. But having spend two grand for this laptop I would like to get Movie Maker to run again with these files that it once worked with. Movie Maker files that actually were created using this computer and this version of Movie Maker. What happened, and what can I do to fix it ??
Your time and input is appreciated.
Cheers !