you should check the site in IE 6 sorry to bring bad news.
IE 6 doesn't support transparent PNG images, there isn't anything I can do about it except put a conditional comment on the page telling people to upgrade.
I'm working in integrating the forums and such, I will be making a bridge between MyBB and WB and I will try to integrate the themes better.
The nav getting lost was kind of the point, and it looks quite dull without a hover image.