The group Immortal Technique has a song called "Dance With The Devil".
This track incorporates a repeating classical music hook...what is the
classical song that plays in the background of "Dance With The Devil"?

Hi kierio,

It's actually not a classical piece.  It's the beginning of the theme
from the 1970 movie "Love Story," starring Ali MacGraw and Ryan
O'Neal.  The theme was written by Francis Lai.

You can verify this from the sample on this catalog page for the soundtrack.

http://www.moviegrooves.com/shop/lovestorysoundtrackfrancis.htm

The recognizable hook does not appear until about 24 seconds into the sample.

Wikipedia has background information on the movie.

http://en.wikipedia.org/wiki/Love_Story

--efn