Well I second the motion about designing for Firefox/Safari/Opera first and IE second. However each browser may implement the standards differently due to bugs, ambigous specifications, and differences of opinion.
This is even more apparent when trying to get "pixel perfect" layout using CSS positioning (ie, position, top/bottom and left/right properties)
I would take cues from other web designers and scrap your layout that relies on CSS positioning and go with the fluid layouts. Put the navigation links in a "column" and float the column to the right. Then put this column and the content in a wrapper and specify width of the wrapper, ie:
<div id="navigation>list of links</div>
<p>Yadda yadda yadda</p>
Then to force the paragraph down you only need to apply a top margin.
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