[css] How to align two divs side by side using the float, clear, and overflow elements with a fixed position div/

This answer may have to be modified depending on what you were trying to achieve with position: fixed;. If all you want is two columns side by side then do the following:

http://jsfiddle.net/8weSA/1/

I floated both columns to the left.

Note: I added min-height to each column for illustrative purposes and I simplified your CSS.

_x000D_
_x000D_
body {_x000D_
  background-color: #444;_x000D_
  margin: 0;_x000D_
}_x000D_
_x000D_
#wrapper {_x000D_
  width: 1005px;_x000D_
  margin: 0 auto;_x000D_
}_x000D_
_x000D_
#leftcolumn,_x000D_
#rightcolumn {_x000D_
  border: 1px solid white;_x000D_
  float: left;_x000D_
  min-height: 450px;_x000D_
  color: white;_x000D_
}_x000D_
_x000D_
#leftcolumn {_x000D_
  width: 250px;_x000D_
  background-color: #111;_x000D_
}_x000D_
_x000D_
#rightcolumn {_x000D_
  width: 750px;_x000D_
  background-color: #777;_x000D_
}
_x000D_
<div id="wrapper">_x000D_
  <div id="leftcolumn">_x000D_
    Left_x000D_
  </div>_x000D_
  <div id="rightcolumn">_x000D_
    Right_x000D_
  </div>_x000D_
</div>
_x000D_
_x000D_
_x000D_

If you would like the left column to stay in place as you scroll do the following:

http://jsfiddle.net/8weSA/2/

Here we float the right column to the right while adding position: relative; to #wrapper and position: fixed; to #leftcolumn.

Note: I again used min-height for illustrative purposes and can be removed for your needs.

_x000D_
_x000D_
body {_x000D_
  background-color: #444;_x000D_
  margin: 0;_x000D_
}_x000D_
_x000D_
#wrapper {_x000D_
  width: 1005px;_x000D_
  margin: 0 auto;_x000D_
  position: relative;_x000D_
}_x000D_
_x000D_
#leftcolumn,_x000D_
#rightcolumn {_x000D_
  border: 1px solid white;_x000D_
  min-height: 750px;_x000D_
  color: white;_x000D_
}_x000D_
_x000D_
#leftcolumn {_x000D_
  width: 250px;_x000D_
  background-color: #111;_x000D_
  min-height: 100px;_x000D_
  position: fixed;_x000D_
}_x000D_
_x000D_
#rightcolumn {_x000D_
  width: 750px;_x000D_
  background-color: #777;_x000D_
  float: right;_x000D_
}
_x000D_
<div id="wrapper">_x000D_
  <div id="leftcolumn">_x000D_
    Left_x000D_
  </div>_x000D_
  <div id="rightcolumn">_x000D_
    Right_x000D_
  </div>_x000D_
</div>
_x000D_
_x000D_
_x000D_