I would assume that VW is simpoly using a semi transparent background image on their menus.
This works on almost all browsersd available today, except IE/win (yes that's right, even IE/mac can handle alpha transparent PNGs correctly).
However you can use some intricate filter stuff to mimic the effect also in IE/win. I don't have my bookmarks available at the moment, but I know there is an article over at ALA (a list apart) explaining how to do this workaround as well as a few other places. I even think it's been mentioned before on this forum.