VML example

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title>Corners</title>
    <style type="text/css">
      html,
      body {
        background: #ccc;
        font-family: Tahoma;
      }
      .container {
        background: #fff;
        padding: 10px;
      }

      .container {
        -moz-border-radius: 10px;
        -webkit-border-radius: 10px;
        border-radius: 10px;
      }
    </style>

    <!--[if lte IE 8]>
      <style type="text/css">
        v\:oval {
          behavior: url(#default#VML);
          display: inline-block;
          position: absolute;
          left: 0;
          top: 0;
          width: 20px;
          height: 20px;
        }
        v\:oval.tl {
          left: 0;
          top: 0;
          right: auto;
          bottom: auto;
        }
        v\:oval.tr {
          left: -10px;
          top: 0;
          right: auto;
          bottom: auto;
        }
        v\:oval.bl {
          left: 0;
          top: auto;
          right: auto;
          bottom: 0;
        }
        v\:oval.br {
          left: -10px;
          top: auto;
          right: auto;
          bottom: 0;
        }

        table.crn {
          margin: 0;
          width: 100%;
          border: none;
          background: none;
        }
        table.crn tbody,
        table.crn tr,
        table.crn td {
          border: none;
          background: none;
        }
        table.crn td {
          padding: 0;
          font-size: 1px;
          line-height: 1px;
          height: 10px;
        }
        table.crn td div {
          width: 10px;
          height: 10px;
          overflow: hidden;
          position: relative;
        }

        .container {
          padding-top: 0;
          padding-bottom: 0;
        }
      </style>
      <xml:namespace ns="urn:schemas-microsoft-com:vml" prefix="v" />
    <![endif]-->
  </head>
  <body>
    <div style="width:500px;margin:5em auto;">
      <!--[if lte IE 8]>
        <table class="crn" width="100%" cellpadding="0" cellspacing="0" border="0">
          <tbody>
            <tr>
              <td width="10">
                <div><v:oval class="tl" fillcolor="white" stroked="false" /></div>
              </td>
              <td style="background:#fff;">&nbsp;</td>
              <td width="10">
                <div><v:oval class="tr" fillcolor="white" stroked="false" /></div>
              </td>
            </tr>
          </tbody>
        </table>
      <![endif]-->
      <div class="container">
        Hello world<br />
        Hello world<br />
        Hello world<br />
        Hello world<br />
        Hello world<br />
      </div>

      <!--[if lte IE 8]>
        <table class="crn" width="100%" height="10" cellpadding="0" cellspacing="0" border="0">
          <tbody>
            <tr>
              <td width="10" height="10">
                <div><v:oval class="bl" fillcolor="white" stroked="false" /></div>
              </td>
              <td height="10" style="background:#fff;">&nbsp;</td>
              <td width="10" height="10">
                <div><v:oval class="br" fillcolor="white" stroked="false" /></div>
              </td>
            </tr>
          </tbody>
        </table>
      <![endif]-->
    </div>
  </body>
</html>

Work in IE6,7,8.

http://msdn.microsoft.com/en-us/library/bb264307%28v=VS.85%29.aspx

To add namespace via js:

<script type="text/javascript">document.namespaces.add("v","urn:schemas-microsoft-com:vml","#default#VML");</script>