var Mac=(navigator.userAgent.indexOf("Mac")!=-1);
var Win=(navigator.userAgent.indexOf("Win")!=-1);
var Netscape=(navigator.appName.indexOf("Netscape")!=-1);
var Explorer=(navigator.appName.indexOf("Explorer")!=-1);
var Version=navigator.appVersion.charAt(0);

if
(Mac && Explorer && Version>="4") 
{document.write('<link rel="stylesheet" href="css/m_ie5.css" type="text/css">');}
else if
(Mac && Netscape && Version=="4")
{document.write('<link rel="stylesheet" href="css/m_nn4.css" type="text/css">');}
else if
(Mac && Netscape && Version>="5")
{document.write('<link rel="stylesheet" href="css/m_nn6.css" type="text/css">');}
else if
(Win && Explorer && Version>="4")
{document.write('<link rel="stylesheet" href="css/w_ie5.css" type="text/css">');}
else if
(Win && Netscape && Version=="4")
{document.write('<link rel="stylesheet" href="css/w_nn4.css" type="text/css">');}
else if
(Win && Netscape && Version>="5")
{document.write('<link rel="stylesheet" href="css/w_nn6.css" type="text/css">');}
else if
(Win)
{document.write('<link rel="stylesheet" href="css/w_etc.css" type="text/css">');}
else
{document.write('<link rel="stylesheet" href="css/etc.css" type="text/css">');}