Disable javascript
Unless there's another way to do it with IE, you need javascript to "disable" the back button. Really what you're doing is replacing the previous element in the history list with the current page. So "history.go(-1)" takes you "back" to where you already are. Actually, I believe there's a few other tricks to do it with javascript, but that's usually how I see it.
The annoying thing is that the ability is there for a very real need. If you're doing a redirect, you need to purge the redirect page from the history so you don't get in a back-and-forth loop.
We have to fight the terrorists as if there were no rules and preserve our open society as if there were no terrorists. -- [link|http://www.nytimes.com/2001/04/05/opinion/BIO-FRIEDMAN.html|Thomas Friedman]