Since IE filters use page as a reference in SRC and the plugin/file
(in WordPress & Drupal) can be in different folders, we need to
extract base url from the CSS file (jquery.fancybox-1.3.1.css). A bit
tricky, but IE behavior solves this problem.

Example:

#fancybox-loading.fancybox-ie div {
    background: transparent;
    behavior:
expression(this.runtimeStyle.filter?'':this.runtimeStyle.filter="progid:DXI mageTransform.Microsoft.AlphaImageLoader(src='"+
(function(){var t=document.getElementsByTagName('link');for(var
i=0;i<t.length;i++){var h=t[i].href.split('?')[0];if(h&&/
jquery.fancybox-1.3.1\\.css$/.test(h)){return
h.replace('jquery.fancybox-1.3.1.css','');}} return '';})() +"../
images/fancybox/fancy_loading.png',sizingMethod='scale')");

It will loop all link tags until it finds jquery.fancybox-1.3.1.css
and ignores '?foo=bar' from that css file and then returns the proper
path to that css file. In my example I'm keeping my css files in css -
folder and all the images in images/fancybox -folder.

Hope this helps to solve WordPress & Drupal problems.

-Jani