Try something like this:

<div id="wrapper">

<div id="header>Put your header code/content here</div>

<ul id="main-nav"><li>Home</li><li>Page</li><li>Page</li></ul>

<div id="main-content">
<p>Let's say this a blog and i want to have ...Umpteen schizophrenic Klingons comfortably bought two obese chrysanthemums. The Klingons fights slightly progressive televisions, although one irascible wart hog easily telephoned two quixotic trailers. Umpteen mats mostly quickly abused five pawnbrokers, and one trailer marries two orifices.</p>
<p>Umpteen schizophrenic Klingons comfortably bought two obese chrysanthemums. The Klingons fights slightly progressive televisions, although one irascible wart hog easily telephoned two quixotic trailers. Umpteen mats mostly quickly abused five pawnbrokers, and one trailer marries two orifices.</p>
</div><!-- end main-content -->

<div id="footer">Footer content</div>

</div><!-- end wrapper -->

Try not to use absolute positioning...and everything should work out fine.
If you want to center all this on the page, check out http://www.bluerobot.com/web/css/center1.html

Hope that helps. Hard to lend a hand without your code. Do you have a link to a dev page? or a JPEG of what you are trying to do?