I mentioned Hack-free CSS for IE the other day. There is one caveat that should be mentioned.

If you’re running multiple versions of Internet Explorer on one machine, all of these versions will act as if they’re the last version installed.

This means that if you have IE6 installed and run IE5 to check, this conditional comment will return true:

<!--[if IE 6]>
  <link rel="stylesheet" type="text/css" href="ie-6.0.css" />
<![endif]-->

and this will return false:

<!--[if IE 5.0]>
  <link rel="stylesheet" type="text/css" href="ie-5.0.css" />
<![endif]-->