How do I detect the user’s browser and apply a specific CSS file?

I need to detect the browser and apply the matched CSS file.

I have created 3 css files: __ie.css, ff.css, opera.css. Now I need to detect the browser in order to include the good one.

I know this

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

But how do I do the same with Firefox and Opera/Chrome?