var ss1 = document.createElement('style');
var def = 'body {color: red;}';
ss1.setAttribute("type", "text/css");
if (ss1.styleSheet) {   // IE
    ss1.styleSheet.cssText = def;
} else {                // the world
    var tt1 = document.createTextNode(def);
    ss1.appendChild(tt1);
}
var hh1 = document.getElementsByTagName('head')[0];
hh1.appendChild(ss1);

via Dynamic SCRIPT and STYLE elements in IE / Stoyan’s phpied.com.

找到三个链接：

http://www.javaeye.com/topic/37745

http://www.cnblogs.com/xujiaci/archive/2007/12/14/994857.html

http://blog.csdn.net/liaoya/archive/2009/01/16/3796217.aspx

然后又发现了这篇，更具重量级的文章：

http://www.stevesouders.com/blog/2009/04/27/loading-scripts-without-blocking/