Code:
HEADER IMG - <img src="images/jpg/header_organic_gray.jpg" width="980" height="85" class="Image100pct" />
LOGO IMG - <img src="../../../assets/jpgs_for_web/dark_logo_smaller_gray.jpg" width="250" height="103" class="logoPosition" />name="NavigationMenu" -->
MENU DIV - <div id="p7PMM_1" class="p7PMMh07">
<ul class="p7PMM">
... bunch of <li>s and a </ul>
I'm fairly convinced that this is a width issue. Since you've got the logo img there and a div just below it with width:auto; and left: 400; if for any reason (and IE6 will find many) the width of the menu div + 250 (logo) + 400 (left margin) is > 980 IE would just move the div to the next line.
On the other hand, since IE6 is fairly picky, it could just be seeing a div next to an image and moving the div to the next line, just because it's IE6 and it can. Not convinced this is the issue, but I wouldn't be surprised either.
A couple of options:
1) wrap the logo in a div floated left and also float the menu div left, hopefully keeping it on the same line.
2) define a width for the menu div rather than using auto (which in a perfect world should work I think but... IE6)
In general I'm not really a fan of using the left: 400; to position things, but that could just be a personal preference.
Best of luck. We all feel your IE6 pain!
~ Nathan