We have several IE specific stylesheets, the thing that makes them IE specific is that they are added using IE comments so that other browsers do not see those files.
If you view the source of the page on any mojo site you will see something like this:
<!--[if lt IE 7]>
<script src="http://www.mojoportal.com/ClientScript/IE7.js" type="text/javascript"></script>
<link rel="stylesheet" href="http://www.mojoportal.com/Data/Sites/1/skins/mojosite-brightside13/IESpecific.css" type="text/css" id="IEMenuCSS" />
<![endif]-->
<!--[if IE 7]>
<script src="http://www.mojoportal.com/ClientScript/IE8.js" type="text/javascript"></script>
<link rel="stylesheet" href="http://www.mojoportal.com/Data/Sites/1/skins/mojosite-brightside13/IE7Specific.css" type="text/css" id="IE7MenuCSS" />
<![endif]-->
The comments hide it from other browsers, the first one is for IE 6 as defined by [if lt IE 7], the second one is only for IE 7.
So you could put your IE specific css in our existing files IESpecific.css and IE7Specific.css or you can add your own using the same technique in layout.master of your skin.
Hope it helps,
Joe