The IT miniseries with John Ritter was ok. The history parts were very well done - the modern day parts, not so much. Of course, that's pretty much the book's problem as well. Plus, the giant spider was much less threatening than Tim Curry as Pennywise - also a problem the book had.
The one thing that mini series had going for it was Tim Curry knocked his creepy demon clown thing out of the park. That mini series had me scared of storm drains for a while.