"Dune II The Building of a Dynasty" OST by Frank Klepacki and Dwight Okahara for Westwood Studios (1992)

Frank Klepacki is also known for the soundtrack for Red Alert 1/2 (Hell March), Tiberian Sun and Renegade.

If you don't have time, just check out the "Introduction" tune, it's only 2:40 but it gets really intense.