+1  A: 

You might want to have a look to this:

http://www.sidesofmarch.com/index.php/archive/2007/04/23/an-ie6-compatible-solution-for-hover

Roberto Aloi
Well well, turns out that was a pretty neat 'hack' by tweaking the selectors with 'hover' to the container. Clever.
o.k.w
A: 

It seems that the following is not effected in IE6

#topNavigation ul li:hover ul
{
    display: block;
}

Can you give the level 2 UL/LI a css class assignment then create a selector for it?

o.k.w
A: 

The :hover pseudoclass is only supported on a elements by IE6, unfortunately.

Check this article for some advice on how to script around the problem.

Mark B