To GuerrilleroHeroico, Crazywill and macmillion - just ween them off it if you can. Install a browser you want them to use on their behalf, then put up desktop and / or taskbar links and remove all instances of the IE links they have (you won't be able to uninstall IE itself and nor should you try).
When you install whatever browser you've chosen, you can move all their bookmarks over from IE if you want. Obviously, they'll have to log into whatever sites they've been using again, but that's no big deal.
Also make sure that you have the browser settings check for automatic updates. I know you've all probably considered this already, but once you've done that they should be set and you can leave them to it.