That was a Sky-TV miniseries which combined The Colour of Magic and The Light Fantastic (which was reasonable, since those two books are effectively two halves of the same story). Tim Curry played the Archchancellor of Unseen University, if I remember right.
It was OK, but it wasn't great. Part of the problem was that a lot of Pratchett's humour comes less from the dialogue, and more from the wordplay, allusions, and asides that he inserts into the narrative, i.e. the parts of a book that don't get translated well onto the screen.
(Plus, much as I enjoy David Jason as an actor, by that point he really was too old (and round!) to play a convincing Rincewind -- IMHO, obviously)