xvid and quicktime

hi,

i am trying to watch some videos, and i saw that i had to download the xvid component to QT. i downloaded it, but it will not let me open it--saying that "the movie could not be opened" and that "the operation could not be completed." when i try to open the xvid files, it says that it is not a movie file. what am i doing wrong/how can i fix this?

thanks!