isMac = (navigator.appVersion.indexOf("Mac")!=-1) ? true : false;
isWin = (navigator.appVersion.indexOf("Win")!=-1) ? true : false;

ie4plus = (document.all) ? true : false;
ns4 = (document.layers) ? true : false;
ns6plus = (!document.layers) && (navigator.userAgent.indexOf('Netscape')!=-1)? true : false; //NS 6,7
opera = (navigator.userAgent.toLowerCase().indexOf("opera") != -1)? true : false;

var styleSheet='';
if (isWin && ie4plus)
{
  styleSheet='<LINK HREF="images/style_win_ie.css" TYPE="textimages" REL="stylesheet">';
}
if (isWin && (ns4 || ns6plus))
{
  styleSheet='<LINK HREF="images/style_ns.css" TYPE="textimages" REL="stylesheet">';
}
if (isMac && ie4plus)
{
  styleSheet='<LINK HREF="images/style_mac_ie.css" TYPE="textimages" REL="stylesheet">';
}
if (isMac && (ns4 || ns6plus))
{
  styleSheet='<LINK HREF="images/style_ns.css" TYPE="textimages" REL="stylesheet">';
}
if (opera)
{
  styleSheet='<LINK HREF="images/style_ns.css" TYPE="textimages" REL="stylesheet">';
}

// Default stylesheet
if (styleSheet=='') styleSheet = '<LINK HREF="images/style_win_ie.css" TYPE="textimages" REL="stylesheet">';

document.write(styleSheet);