Conditional comments only work in Internet Explorer, and are thus excellently suited to give special instructions (CSS and JavaScript) meant only for Internet Explorer. They are supported from Internet Explorer 5 onwards.
<!--[if IE]>
This is Internet Explorer
<![endif]-->
<!--[if IE 5]>
This is Internet Explorer 5
<![endif]-->
<!--[if IE 5.0]>
This is Internet Explorer 5.0
<![endif]-->
<!--[if IE 5.5]>
This is Internet Explorer 5.5
<![endif]-->
<!--[if IE 6]>
This is Internet Explorer 6
<![endif]-->
<!--[if IE 7]>
This is Internet Explorer 7
<![endif]-->
<!--[if gte IE 5]>
This is Internet Explorer 5 and up
<![endif]-->
<!--[if lt IE 6]>
This is Internet Explorer lower than 6
<![endif]-->
<!--[if lte IE 5.5]>
This is Internet Explorer lower or equal to 5.5
<![endif]-->
<!--[if gt IE 6]>
This is Internet Explorer greater than 6
<![endif]-->
Note the special syntax:
not-operator (!):
<!--[if !IE 6]-->
greater than:
<!--[if gt IE 6]-->
greater than or equal to:
<!--[if gte IE 6]-->
less than:
<!--[if lt IE 6]-->
less than or equal to:
<!--[if lte IE 6]-->
