Simply copy the below code into the head of your PHP document. Remember, the page your working on must have a .php extension, and your server must be running PHP. Like in the above code, you need to specify the path of the two stylesheets. I've done so below in red.

<?
if ($name = strstr ($HTTP_USER_AGENT, "MSIE"))
{
?>
<link rel="stylesheet" xhref="internet-explorer-stylesheet.css">
<?
}
else if ($name = strstr ($HTTP_USER_AGENT, "Netscape"))
{
?>
<link rel="stylesheet" xhref="netscape-stylesheet.css">
<?
}
else
{
?>
<link rel="stylesheet" xhref="other-stylesheet.css">
<?
}
?>

Credit: www.spoono.com 

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