if ( screen.width >= 1280){ 
document.write('<link href="css/script_float_menu_1280.css" rel="stylesheet" type="text/css" media="screen" />'); 
} else if ( screen.width >= 1024){ 
document.write('<link href="css/script_float_menu_1024.css" rel="stylesheet" type="text/css" media="screen" />'); 
} else if ( screen.width >= 800){ 
document.write('<link href="css/script_float_menu_800.css" rel="stylesheet" type="text/css" media="screen" />'); 
}