2 column div layout: right column with fixed width, left fluid

See http://www.alistapart.com/articles/negativemargins/ , this is exactly what you need (example 4 there).

<div id="container">
    <div id="content">
        <h1>content</h1>
        <p>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.  Phasellus varius eleifend tellus. Suspendisse potenti. Class aptent taciti sociosqu ad litora torquent per conubia nostra, per inceptos hymenaeos. Nulla facilisi. Sed wisi lectus, placerat nec, mollis quis, posuere eget, arcu.</p>
        <p class="last">Donec euismod. Praesent mauris mi, adipiscing non, mollis eget, adipiscing ac, erat. Integer nonummy mauris sit amet metus. In adipiscing, ligula ultrices dictum vehicula, eros turpis lacinia libero, sed aliquet urna diam sed tellus. Etiam semper sapien eget metus.</p>
    </div>
</div>

<div id="sidebar">
    <h1>sidebar</h1>
    <ul>
        <li>link one</li>
        <li>link two</li>
    </ul>
</div>

---

#container {
    width: 100%;
    background: #f1f2ea url(background.gif) repeat-y right;
    float: left;
    margin-right: -200px;
}
#content {
    background: #f1f2ea;
    margin-right: 200px;
}
#sidebar {
    width: 200px;
    float: right;

Best to avoid placing the right column before the left, simply use a negative right-margin.

And be "responsive" by including an @media setting so the right column falls under the left on narrow screens.

<div style="background: #f1f2ea;">
  <div id="container">
    <div id="content">
        <strong>Column 1 - content</strong>
    </div>
  </div>
  <div id="sidebar">
    <strong>Column 2 - sidebar</strong>
  </div>
<div style="clear:both"></div>

<style type="text/css">
#container {
    margin-right: -300px;
    float:left;
    width:100%;
}
#content {
    margin-right: 320px; /* 20px added for center margin */
}
#sidebar {
    width:300px;
    float:left
}
@media (max-width: 480px) {
    #container {
        margin-right:0px;
        margin-bottom:20px;
    }
    #content {
        margin-right:0px;
        width:100%;
    }
    #sidebar {
        clear:left;
    }
}
</style>

Remove the float on the left column.

At the HTML code, the right column needs to come before the left one.

If the right has a float (and a width), and if the left column doesn't have a width and no float, it will be flexible :)

Also apply an overflow: hidden and some height (can be auto) to the outer div, so that it surrounds both inner divs.

Finally, at the left column, add a width: auto and overflow: hidden, this makes the left column independent from the right one (for example, if you resized the browser window, and the right column touched the left one, without these properties, the left column would run arround the right one, with this properties it remains in its space).

Example HTML:

<div class="container">
    <div class="right">
        right content fixed width
    </div>
    <div class="left">
        left content flexible width
    </div>
</div>

CSS:

.container {
   height: auto;
   overflow: hidden;
}

.right {
    width: 180px;
    float: right;
    background: #aafed6;
}

.left {
    float: none; /* not needed, just for clarification */
    background: #e8f6fe;
    /* the next props are meant to keep this block independent from the other floated one */
    width: auto;
    overflow: hidden;
}​​

Example here: http://jsfiddle.net/jackJoe/fxWg7/