引用jQuery的插件jquery.pseudo.js
插件内容：

(function($){

    var patterns = {
        text: /^['"]?(.+?)["']?$/,
        url: /^url\(["']?(.+?)['"]?\)$/
    };

    function clean(content) {
        if(content && content.length) {
            var text = content.match(patterns.text)[1],
                url = text.match(patterns.url);
            return url ? '<img src="' + url[1] + '" />': text;
        }
    }

    function inject(prop, elem, content) {
        if(prop != 'after') prop = 'before';
        if(content = clean(elem.currentStyle[prop])) {
            $(elem)[prop == 'before' ? 'prepend' : 'append'](
                $(document.createElement('span')).addClass(prop).html(content)
            );
        }
    }

    $.pseudo = function(elem) {
        inject('before', elem);
        inject('after', elem);
        elem.runtimeStyle.behavior = null;
    };

    if(document.createStyleSheet) {
        var o = document.createStyleSheet(null, 0);
        o.addRule('.dummy','display: static;');
        o.cssText = 'html, head, head *, body, *.before, *.after, *.before *, *.after * { behavior: none; } * { behavior: expression($.pseudo(this)); }';
    }

})(jQuery);

引入插件后，即可在ie8中使用伪类选择器。