There was a Dune RPG, published by Last Unicorn Games, but it was a limited edition print, and not well representated throughout the roleplaying world. This site (
http://www.darkholmekeep.net/dune/main.cfm) has more information (as well as some extracts).
Hmm, I thought WotC had the rights, and there is some speculation around various Dune fansites about a d20 Dune RPG, but that is as yet unconfirmed.
Cheers,
TGHO