Blocking port 80 and 443 would then cause all browsers to not connect. From what I am getting from the post, and Candidog, correct me if I'm wrong, is that IE is the only thing you want blocked.
Something else you could try (I've never attempted this, so I don't know the results) would be to change the permissions on the Internet Explorer directory to not allow users the ability to read, or read & execute. I'm looking for the script I did about 2 years ago that did something like this, and I will post back.