Put the divs you want to scroll in a table like so:
<div style='width:1000;border:2 solid red;overflow-x:auto'>
   <table><tr>
      <td><div style='width:300;height:200;border:1 solid black'>Cell 1 </div></td>
      <td><div style='width:300;height:200;border:1 solid black'>Cell 2 </div></td>
      <td><div style='width:300;height:200;border:1 solid black'>Cell 3 </div></td>
      <td><div style='width:300;height:200;border:1 solid black'>Cell 4 </div></td>
      <td><div style='width:300;height:200;border:1 solid black'>Cell 5 </div></td>
   </tr></table>
</div>
Ron
Edit:
I tried 3 of these suggested solutions - they all work fine in Google Chrome - but the first one (container1) doesn't work in IE (go figure) - so the SPAN solution gets my vote :-) :
<html>
<body>
<style>
div#container1 
   {
   height: 275px;
   width: 100%;
   overflow: auto;
   white-space: nowrap;
   border:2 solid red;
   }
div#container1 div.block 
   {
   width: 300px;
   height: 200px;
   display: inline-block;
   border: 1 solid black;
   }
div#container2 
   {
   height: 275px;
   width: 100%;
   overflow: auto;
   white-space: nowrap;
   border:2 solid red;
   }
div#container2 span.block 
   {
   width: 300px;
   height: 200px;
   display: inline-block;
   border: 1 solid black;
   }
div#container3 
   {
   height: 275px;
   width: 100%;
   overflow: auto;
   white-space: nowrap;
   border:2 solid red;
   }
div#container3 div.block 
   {
   width: 300px;
   height: 200px;
   display: inline-block;
   border: 1 solid black;
   }
</style>
<p>
<div id='container1'>
      <div class='block'>Cell 1 </div>
      <div class='block'>Cell 2 </div>
      <div class='block'>Cell 3 </div>
      <div class='block'>Cell 4 </div>
      <div class='block'>Cell 5 </div>
</div>
<p>
<div id='container2'>
      <span class='block'>Cell 1 </span>
      <span class='block'>Cell 2 </span>
      <span class='block'>Cell 3 </span>
      <span class='block'>Cell 4 </span>
      <span class='block'>Cell 5 </span>
</div>
<p>
<div id='container3'>
   <table><tr>
      <td><div class='block'>Cell 1 </div></td>
      <td><div class='block'>Cell 2 </div></td>
      <td><div class='block'>Cell 3 </div></td>
      <td><div class='block'>Cell 4 </div></td>
      <td><div class='block'>Cell 5 </div></td>
   </tr></table>
</div>
</body>
</html>
Edit 2:
I ran this test page through browsershots.org, to see how different browsers handle it.
Conclusion: Browser compatibility sucks. :-)
http://browsershots.org/http://dot-dash-dot.com/files/test_div2.htm
The table solution worked more often - but the span option (which is cleaner) only broke on browsers I've never heard of. :-)