Once IE has processed all the styles loaded with the page, the only reliable way to add another stylesheet is with document.createStyleSheet(url)
See the MSDN article on createStyleSheet for a few more details.
url="style.css";
if (document.createStyleSheet)
{
document.createStyleSheet(url);
}
else
{
$('<link rel="stylesheet" type="text/css" href="' + url + '" />').appendTo('head');
}