HTML5 compatibility issues with older browsers. Please help!

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1

I designed an HTML5 site, but when it renders in older versions of Internet Explorer the layout changes. I am not sure what is wrong with it. I’ll post the link and you can view the source code. I’ll also post my css. Disability

@charset "utf-8";
address, article, aside, canvas, details, figcaption, figure, footer, header, hgroup, menu, nav, section, summary {
	display: block;
	background-color: #FFF;
}
html {
	background-color: #D0D0D0;
}
.clearfix:before, .clearfix:after {
	content: "\\0020";
	display: block;
	height: 0;
	overflow: hidden;
}
.clearfix:after {
	clear: both;
}
.clearfix {
	zoom: 1;
}
body {
	width: 1000px;
	padding: 0;
	text-align:left;
	position: relative;
	font-family: Verdana, Geneva, sans-serif;
	font-size: 100%;
	background-color: #FFF;
	margin-top: 0;
	margin-bottom: 0;
	height: auto;
}
.table_header {
	color: #000;
	background-color: #465880;
	text-align: center;
}
.table_odd_row {
	background-color: #D8D8D8;
	text-align: center;
}
.table_even_row {
	text-align: center;
}
.table_first_column {
	text-align: left;
}
section {
	float: right;
	width: 835px;
	padding-right: 10px;
}
#SideBarAds {
	float: left;
	width: 125px;
	height: 100%;
	padding-top: 75px;
	padding-right: 10px;
	padding-left: 10px;
}
#MainColumnAd {
	float: right;
	width: 835px;
	padding-right: 10px;
	padding-left: 10px;
	padding-bottom: 10px;
	padding-top: 10px;
}
footer {
	width: 1000px;
	padding-top: 2em;
	float: right;
	text-align: center;
	margin-bottom: 10px;
}
h1 {
	font-size: 1.5em;
	color: #465880;
}
h2 {
	font-size: 1.2em;
	color: #465880;
}
h3 {
	font-size: 1em;
	font-style: italic;
	color: #465880;
}
.body_image {
	padding: 10px;
	float: right;
}
#DurationOfWorkTitle {
	font-weight: bold;
	background-color: #09F;
	text-align: center;
}
2

For older browsers you need JavaScript if you want to use HTL5 elements, because they reject elements they don’t recognize. You could check out Modernizr or the [URL=“http://ejohn.org/blog/html5-shiv/”]HTML5 Shiv, for example.

3

Do you have an experience with either of them? I tried Modernizr, but it didn’t work. I’m not sure if I did it right.