I found your menu plugin (THANK YOU) for a WordPress site I’m working on. When I installed it, IE7 wasn’t showing the dropdowns (as some have already posted), so I followed your advice and started removing all the styling associated with that area of the site.
The thing that "ruined me up" was a global reset. It wasn’t until I removed *{background:transparent;} that the dropdowns appeared.
I’m not even going to attempt to figure that one out.
I hope this helps if you haven’t run into this before.