A tiny polyfill that adds support for opacity CSS rules to IE8, IE7 and IE6. jQuery not required.
Note that this polyfill does not work with inline styles. Another requirement for IE6 and 7 is to have the stylesheets hosted on the same domain as the website. Stylesheets that don't need opacity fixing may be placed anywhere.
Include the script in your header, optionally with the IE conditional tag.
<!--[if lte IE 8]><script src="jquery.ie-opacity-polyfill.js"></script><![endif]-->
Now you can use opacity in CSS like you would in a real browser (without the silly filter syntax).
a.transparentLink { opacity: 0.5; }