+2  A: 

Well according to the feature list, IE7.js adds support for the :hover pseudo-selector for all elements in IE6. This means that Whatever:Hover htc is not needed since it provides the same type of functionality.

As far is whether you'll need too keep the Suckerfish JavaScript for your CSS menus or not, I don't know. However, since all of the features needed for CSS menus to work are included with IE7.js, I don't think it would be necessary.

Your best option would be to remove those 2 scripts from your site and see what happens.

There are so many edge cases that eventually these scripts designed to pick up the slack for IE6 will miss some small area that was somehow missed. You'll need to do good QA no matter what option you go with. If you use just IE7.js, at least it will be easy to narrow down bugs to 1 JavaScript file, rather than 2-3.

Dan Herbert