if (window.navigator.userAgent.indexOf("MSIE")>=1) 
{  
var IE800="style4.css"; 
var IE1024="style8.css"; 
var IEother="style.css"; 
ScreenWidth(IE800,IE1024,IEother) 
} 
else{ 
if (window.navigator.userAgent.indexOf("Firefox")>=1) 
{ 
var Firefox800="style4.css"; 
var Firefox1024="style8.css"; 
var Firefoxother="style.css"; 
ScreenWidth(Firefox800,Firefox1024,Firefoxother) 
} 
else{ 
var Other800="style4.css"; 
var Other1024="style8.css"; 
var Otherother="style.css"; 
ScreenWidth(Other800,Other1024,Otherother) 
} 
}

function ScreenWidth(style4,style8,style){ 
if ((screen.width == 800) && (screen.height == 600)){ 
setActiveStyleSheet(style4); 
}
else if((screen.width == 1024) && (screen.height == 768)){ 
setActiveStyleSheet(style8); 
}
else{ 
setActiveStyleSheet(style); 
}
} 

function setActiveStyleSheet(title){ 

document.getElementsByTagName("link")[2].href="../css/"+title; 
}