var myCSS = "screen";
var agent = navigator.userAgent.toLowerCase();

if(agent.indexOf("netscape") != -1){
//code to show Safari Stylesheet
myCSS = "mozilla";
}
else if(agent.indexOf("apple") != -1){
//code to show Safari Stylesheet
myCSS = "mozilla";
}
else if(agent.indexOf("msie") != -1){
//code to show Safari Stylesheet
myCSS = "msie";
}
else if(agent.indexOf("mozilla") != -1){
//code to show Safari Stylesheet
myCSS = "mozilla";
}
else if(agent.indexOf("explorer") != -1){
//code to show Safari Stylesheet
myCSS = "msie";
}
else if(agent.indexOf("safari") != -1){
//code to show Safari Stylesheet
myCSS = "mozilla";
}
else if(agent.indexOf("opera") != -1){
//code to show opera Stylesheet
myCSS = "mozilla";
}
document.write('<link rel="StyleSheet" type="text/css" href="styles/'+ myCSS +'.css">');