Hi Christian,
Even in Firefox the submenus are displaced to the left. It would require some doing and time to analyze your code, so, I warmly recommend to refrain from excessive JavaScript and compose the menu in pure HTML with a little help of CSS, such as margins and paddings.
All versions of IE6 are having problems with rendering CSS ever since. Your website, at this time, is simple, so, keep it simple in code, thus cross-platform compatible.
I am a freelance web designer serving small to medium sized enterprises, and someday soon, I will no longer check my code with IE6.
Cheers
Robert