I have done some testing of the menu in IE 6, and IE8 in compatibility mode. I was able to make it behave a little better at least in IE 8 compatibility mode, I was not able to test the update in IE 6.
The update was for the css for the level 1 UL LI, here is the specific thing that I changed that seemed to get it to work correctly:
UL#cssmw UL LI
You should give this a try to see if you get it worked out. I think the solution will be along these lines and you will need to make adjustments and test to get it worked out.