changing from fixed to fluid

I’m trying to make the middle section of my site fluid so that i’m not limited to 500px. Any help would be appreciated because I’m a css newb and I’ve just been getting no where with this:

/*
Theme Name: Scratch
*/

body, h1, h2, h3, h4, h5, h6, address, blockquote, dd, dl, hr, p, form{
	margin: 0;
	padding: 0;
}

body{
	font-family: Arial, Helvetica, Georgia, Sans-Serif;
	font-size: 12px;
	text-align: center;
	vertical-align: top;
        background: #666 url(images/bg_body.gif);
	color: #fff;
}

h1, h2, h3, h4, h5, h6{
	font-family: Arial, Helvetica, Georgia, Sans-Serif;
	font-size: 16px;
}

a{
	text-decoration: underline;
	color: #105cb6;
}

a:hover{ text-decoration: none; }

a img{ border: 0; }

abbr, acronym{ border: 0; }

address, dl, p{ padding: 10px 0 0; }

blockquote{
	margin: 10px 10px 0;
	background: #fffada url(images/bg_blockquote.gif) no-repeat 5px 7px;
	color: #736926;
}

blockquote p{
	padding: 10px 10px 10px 20px;
}

blockquote blockquote{
	margin: 10px 20px;
	background: #fff;
	color: #333;
}

blockquote blockquote p{ padding: 10px; }

code{
	background: #f9f9f9;
}

dt{
	font-weight: bold;
}

dd{
	padding: 0 0 5px 15px;
}

hr{
	clear: both;
	margin: 15px 0 5px;
	width: 100%;
	border: 0;
	height: 1px;
	text-align: left;
	background: url(images/bg_comment_bottom.gif) no-repeat;
}

small{
	font-size: 10px;
}

input, textarea{
	font-family: Arial, Helvetica, Georgia, sans-serif;
	font-size: 12px;
	padding: 2px;
}

input#author, input#email, input#url, textarea#comment{
	border: 1px solid #cbb945;
	background-color: #fffadb;
	padding: 3px;
}

input#author, input#email, input#url{
	margin: 0 5px 0 0;
}

#container, #header, #menu, #menu ul li, #menu ul li a, #pagetitle, h1, #syndication, .pagewrapper, .page, .wrapper, .narrowcolumnwrapper, .narrowcolumn, .content, .post, .entry, .browse, sidebar{
	text-align: left;
	vertical-align: top;
}

#container{
	margin: 0 auto;
	width: 904px;
	padding: 0 0 0;
}

#header{
	margin: 0 0 10px;
	float: left;
	width: 904px;
	height: 210px;
	background: url(images/bg_header.gif) no-repeat left bottom;
	color: #333;
}

#menu ul{
	margin: 0;
	padding: 0 0 0 10px;
	list-style: none;
}

#menu ul li{
	float: left;
	margin: 0 5px 0 0;
	font-size: 14px;
	font-weight: bold;
	background: url(images/bg_tab_right.gif) no-repeat right top;
	color: #325b0a;
}

#menu ul li a{
	display: block;
	padding: 14px 20px 10px;
	text-decoration: none;
	background: url(images/bg_tab_left.gif) no-repeat left top;
	color: #325b0a;
}

#menu ul li a:hover{
	text-decoration: underline;
}

#pagetitle{
	clear: both;
	width: 904px;
	height: 155px;
}

#pagetitle h1{
	padding: 36px 28px 0;
	font-size: 24px;
	font-weight: bold;
	letter-spacing: 1px;
	text-transform: uppercase;
	color: #fff;
}

#pagetitle h1 a{
	text-decoration: none;
	color: #fff;
}

#syndication{
	float: left;
	padding: 15px 31px 0;
	color: #999;
}

#syndication a{ color: #666; }

#syndication a.feed{
	padding: 0 0 0 19px;
	background: url(images/feed_icon.png) no-repeat 0 1px;
}

/*#searchbox{
	float: right;
	padding: 10px 31px 0;
}

#searchbox input#s{
	border: 1px solid #ddd;
	padding: 3px;
	background: #fff;
}

#searchbox input#searchsubmit{ height: 24px; }
*/

.pagewrapper{
	margin: 0 0 10px;
	float: left;
	width: 904px;
	background: #fff url(images/bg_page_bottom.gif) no-repeat left bottom;
	color: #333;
}

.page{
	float: left;
	padding: 0 5px 5px;
	background: url(images/bg_page_top.gif) no-repeat;
}

.wrapper{ /* This wrapper class appears only on Page and Single Post pages. */
	float: left;
	width: 600px;
}

.narrowcolumnwrapper{
	margin: 5px 0 0;
	float: left;
	width: 500px;
	background: #fff url(images/bg_narrowcol.gif) repeat-y;
}

.narrowcolumn{
	float: left;
	width: 500px;
	background: url(images/bg_narrowcol_bottom.gif) no-repeat left bottom;
}

.content{
        float: left;
	width: 500px;
	background: url(images/bg_narrowcol_top.gif) no-repeat left top;
}

.post{
	padding: 9px 16px 15px;
	line-height: 18px;
}

.post h2{
	padding: 0 0 2px;
	font-size: 16px;
	font-weight: bold;
	line-height: 27px;
        text-align: center;

}

.post h2 a{
	text-decoration: none;
	color: #105cb6;
	border-bottom: 1px solid #75abea;
}

.post img{
	padding: 4px;
	border: 1px solid #ddd;
	background: #fff;
}

.post img.alignleft{
	float: left;
	margin: 5px 10px 0 0;
}

.post img.alignright{
	float: right;
	margin: 5px 0 0 10px;
}

.post img.wp-smiley{
	padding: 0;
	border: 0;
	background: none;
}

.entry{}

.entry h1, .entry h2, .entry h3, .entry h4, .entry h5, .entry h6{
	padding: 9px 0 0;
}

.entry h1{
	font-size: 20px;
	line-height: 30px;
}

.entry h2{ line-height: 18px; }

.entry h3{ font-size: 14px; }

.entry h4{ font-size: 12px; }

.entry h5{ font-size: 11px; }

.entry h6{ font-size: 10px; }

.postinfo{
	font-size: 11px;
	color: #999;
}

.postinfo a{
	color: #578cca;
}

.postdate{ color: #a12a2a; }

.browse{
	border-top: 1px solid #bdbdbd;
	padding: 15px 16px;
	line-height: 18px;
}

.sidebar, .obar{
	margin: 0 0 0 5px;
	float: right;
	width: 192px;
	line-height: 18px;
}

.obar{
	margin: 0 0 5px 0;
	float: left;
}

.sidebar ul, .obar ul{
	margin: 0;
	padding: 0;
	list-style: none;
}

.sidebar ul li, .obar ul li{
	margin: 5px 0 0;
	padding: 9px 16px 15px;
	background: url(images/bg_ul_li.gif) no-repeat left top;
}

.sidebar ul li.widget_search, .obar ul li{
	padding: 15px 16px;
}

.sidebar ul li h2, .obar ul li h2{
	font-size: 20px;
        font-weight: bold;
	line-height: 16px;
	color: #cc9900;
}

.sidebar ul ul li, .obar ul ul li{
	margin: 0;
	padding: 0px 0 3px;
	background: none;
}

.sidebar ul ul ul, .obar ul ul ul{ padding: 3px 0 0; }

.sidebar ul ul ul li, .obar ul ul ul li{
	padding: 0px 0px 3px 15px;
	background: url(images/bg_arrow_right.gif) no-repeat 0px 8px;
}

.sidebar ul ul ul ul li, .obar ul ul ul li{
	background: url(images/bg_arrow_right_2.gif) no-repeat 0px 8px;
}

/* COMMENTS TEMPLATE */

.post h3#comments, .post h3#respond{
	padding: 0 0 2px 19px;
	line-height: 27px;
	background: url(images/user_comment.gif) no-repeat 0 6px;
	color: #e45b00;
}

.post h3#respond{
	background: url(images/add_comment.gif) no-repeat 0 6px;
	color: #333;
}

ol.commentlist{
	margin: 0 0 11px;
	padding:0;
	list-style: none;
}

ol.commentlist li{
	padding: 13px 0;
	background: url(images/bg_comment_bottom.gif) no-repeat left bottom;
}

ol.commentlist li .commentmetadata{
	font-size: 11px;
	color: #546477;
}

ol.commentlist li .commentmetadata a{
	color: #546477;
}

form#commentform small{
	font-size: 11px;
}

Any suggestions would be great! thanks