By I've just watched the second part of Sky's adaptation of The Colour Of Magic and thoroughly enjoyed it. I would class myself as a fan of Pratchett's work; not an absolute fanatic, but somebody with more than a passing familiarity and can honestly say that I'm happy with the job they've done with this adaptation.
Although nothing has been confirmed it's very likely that more adaptations will follow; David Jason has already said he would like to do more. On a related note, Sam Raimi owns the rights for The Wee Free Men and although no further details are available, it's expected to hit cinemas in 2010.
There was another Pratchett book made into a film, though I can't remember what it is (not The Hogfather)
Aha! Just had a look on IMDB and Wyrd Sisters was made into a TV program in 1997. Again it had Christopher Lee as DEATH. On closer inspection it was an animation. Not sure if it is worth a look. Might do.
It was made by Cosgrove Hall for Channel 4; they also did Soul Music.