Help for Movie Maker Here.....
Vista is little more than a half baked operating system that Microsoft hurried into release for the US Gov. it has built in a computer equivalent to a lojack .
I might be able to help, due to the unstable nature of this software,and it's inability to get along with other programs, there are usually work around solutions when you have these types of problems.
I assume because of your statement about un install /reinstall not being an option, that this is an OEM installation of the movie maker software that came with the computer pre loaded.
Usually in this circumstance you were instructed to create "restore Disks" in case you have a terminal crash or corruption, or a restore disk was provided with the purchase, either way you can do what is called a destructive install of the operating system or a non destructive install, this option was also included with the XP systems, you would access this option upon reboot, after selecting to recover, options become available for destructive or non destructive installation, of course choose "NON" or you will lose all data on the disk,and send it back to the day you purchased it.
This option will restore all original software packaged with the operating system including the Movie Maker,,,,,
If that is not an option then go to my computer icon and open,when looking there you should see a drive lettered "D" this drive was created upon installation as a safeguard, it contains a complete copy of all critical system files, and can be used to restore functionality to corrupt systems, it is usually kept on a part of the disk that can't be accessed or moved making it always available.
If both of these options are out of reach or your skill level, then a much simpler resolution may be found, by doing a Google search using these key words in the search.... Movie Maker,Vista, data cabs, restore, location.
You could also add Microsoft or Help to that list of search words, but what you should find will be a Microsoft page or a hacker page that will instruct you how to browse the original CD or restore CD, and locate the cab files which contain the Movie Maker software, these cab files are usually numbered and many, but the location of the Movie Maker installation will be in one of them,and once located can be re installed directly from those cab files...
One more option I can think of would be to use the restore to previous date option, choose the date 1 day prior to your noticing the Movie Maker failing, and select restore to that date, you will not lose any accumulated files or work but it will undue any system updates that took place between then and now,including newly installed programs,and they would need to be re updated but that's just a couple of Microsoft update clicks ,and a fair trade for the fix I think, but at least one of these options should be available to you ,and get you back on your movie making way.....
Last option I can think of would be to go to my computer and open , right click on drive "C" and select options a pop up will deploy, then on the tabs up top choose tools, at that point select error checking scan now, and another pop up will deploy put a tick in both boxes 1. automatically fix file system errors,and 2. scan for and attempt recovery of bad sectors.
This will tell you that it can't be done right now due to the operating system running ,and it will ask if you would like to preform this action upon re boot, select yes and reboot......you will want to start with the easiest,and least destructive of these options and work your way down the list........
If you have a need for more details or another possible option, just reply to this, by then I will have done a search and might know more about it, but I think one of these will be your fix......I hope this helps and good luck.....