Windows Movie Maker is normally located at C:\Program Files\Movie Maker\moviemk.exe
Are you sure you didn't just accidentally delete the shortcut? If that's the case it's easy to resolve. Otherwise if you did delete the program, you're SOL as it's part of the OS and isn't separately (un)installable.
stlcardinals: Live Movie Maker is only for Vista and later. The OP is on XP