Unfortunately IE6-IE8 do not support rounded borders. Instead you would need to use something like CSS3PIE.
IE9 however DOES understand border-radius
Update further to comment that it 'won't work' - here is a quick step-by-step (this is a very simple, high-level sample.
- Download CSS3PIE at http://css3pie.com/download-latest
- Save the .htc file in the root of your site
Lets say you have a div with the id of foo:
<div id="foo">Hello, I'm rounded</div>
Your CSS for this could be:
#foo { width: 500px; height: 200px; background: blue; -moz-border-radius: 12px; /* FF1-3.6 */
-webkit-border-radius: 12px; /* Saf3-4, iOS 1-3.2, Android <1.6 */
border-radius: 12px; /* Opera 10.5, IE9, Saf5, Chrome, FF4, iOS 4, Android 2.1+ */ }
You simply need to add one more rule to the bottom of that CSS, as follows behavior: url(/PIE.htc);
This will cause CSS3 to apply your border-radius rules to IE6-8.