Is it possible to use
var script = document.createElement('link');
script.href = 'theme/style/ie/manageleads.css';
script.rel = 'stylesheet';
script.type = 'text/css';
document.getElementsByTagName('head')[0].appendChild(script);
and for it to only be active if the browser is IE8?
http://api.jquery.com/jQuery.browser/
Note that IE8 claims to be 7 in Compatibility View.
if ($.browser == 'msie' && (parseInt($.browser.version) == 8 || parseInt($.browser.version) == 7))
{
// Do something IE8-only in here
}