Very easy way is use <div id> tags and extern style.css file.
e.g. this code in HTML file:
In header:
<link rel="stylesheet" type="text/css" href="style.css" />
Body:
<body>
<div id="container">
<div id="menu">
blah blah
</div>
<div id="content">
blah blah
</div>
</div>
</body>
and CSS:
#container {
width: 500px;
margin: 0 auto;
}
#menu {
width: 200px;
height: 600px;
float: left;
background-color: #c6d9f0;
}
#content {
width: 300px;
height: 600px;
float: left;
background-color: #ffffff;
}
I hope, that I understand right, what you want. :)