+2  A: 

Without the HTML it's hard to say but you shouldn't have position: absolute and float: left on the same element - that doesn't really make sense.

You probably shouldn't be using position anywhere in your stylesheet for this. It's usually something to stay away from unless you're scripting.

Edit: give this a go:

<style>

#greenback {
    width: 800px ;
    height: 250px ;
    background-color: #7EBB11 ;
    border: 3px solid #112D82 ;
}

#picright {
    float: right;
    display: block;
    margin: 11px 11px 11px 20px;
    width: 50%;
    height: 218px;
    border: 3px solid white;
}

#billboard  {
    width: 45% ;
    height: 99% ;
    border: 2px solid blue;
    float: right;
}

#billboard p {
    text-align: center;
    margin: 0;
    border: 1px solid red;
    margin-top: 50px;
    font-family: Optima, Calibri, Candara, Century-Gothic, Arial, sans-serif;
    font-size: 160% ;
    color: #ffffff ;
}
</style>

<div id="greenback">
    <img src="kids.jpg" alt="kids" id="picright" />
    <div id="billboard"><p>We help businesses,<br>communities and nature<br>take better care<br>of each other.</p></div>
</div>
Greg
that makes sense, thanks RoBorg.. the html is at the bottom of the posting under the css
Ahh so it is... silly me
Greg
Well, removing all the position statements didn't mess anything up in FF at least, let's see what happens with IE!
RoBorg, you are a legend! I'll buy you an e-beer for that (though they never taste as good...) IE 6 and 7 both look like FF. It's so good and so simple I'm in shock. Still waiting on browsershots.org to render IE8. I wonder if this trick will work on other divs styling other pages on the site...
annakata, thanks so much for the edited code - it fixed my centering issue as well and it looks great on IE6,7 and 8 - and using the red line as a teaching tool is a beautiful touch. The page now looks great on IE6,7 and 8 too. Much appreciated. This is such a nice forum. Now to the next divs..!