I've not installed IE8 yet, so no idea what issues you might run into with the Menu Writer menus. However, if you were to post a link to a page that is having this issue, someone would be able to take a look at the page to see what issues their might be with the menu.
If everything is working in the other browsers and not in IE8 then generally speaking all of the files are in place, so it may be an IE8 issue or potentially some scripting issue.