The dropdown menu on my Drupal 7 site [tinyurl.com...] works fine in other browsers but in Internet Explorer 7, only the first sub-menu item is displayed correctly and items below this are written vertically instead of horizontally.
Maybe some help is on the way. In the meantime the only suggestion I have, while I also experienced dropdown menu problems in Internet Explorer, is change your doctype. My problems were solved once I used the strict type.
As webprutser says, doctype's can resolve a lot of issues, but from your description it might also be the code or selectors used to layout the sub-menu items. Your link goes to the front page of WebmasterWorld - not a bad thing ;) - and I can't see the issue in the screenshot. So could you post the menu css and html so we can take look at the code itself? My "welcome" link explains how to reduce code for posting if you're not sure what is required.